Q.1What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid.

When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity,
i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

Q.2 Why and when does a current carrying conductor kept in a magnetic field experience force? List the factors on which direction of this force depends?
Answer. The drifting of free electrons of a conductor in a definite direction causes the current to flow through it. When such conductor is placed in a uniform magnetic field, each drifted electron of a conductor experience a magnetic force. This force is collectively experience by a conductor as a whole. Hence a current carrying conductor kept in a magnetic field experience a force. The direction of magnetic force depends on
(i) direction of current through the conductor, and
(ii) direction of magnetic field.

Q.3 How is the strength of magnetic field near a straight current-conductor
(i) related to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer.
(i) The strength of magnetic field around a straight current conductor increases
on increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Q.4 Explain any two situations that can cause electrical hazards in domestic circuits.
Answer. (i) Connecting too many electrical devices to a single socket or in the extension
cord for any length of time draws high current from the mains that will exceed the current rating of connecting wires. The wires cannot withstand such a high current and melt and may cause fire.
(ii) Most electrical hazards in domestic circuits are caused by the faulty electrical outlets, old and out-dated appliances. The chances of short circuit i.e., contact of live wire and neutral wires with each other due to damage in their insulation or some fault in the appliances are very high. It may result spark at the contact point which may even cause fire,

Q.5 List in tabular form two major differences between an electric motor and a
generator.
Answer.

Q.6 Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer.
(a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.

Q.7 Consider a circular loop of wire lying in the plane of the paper. Let the current
pass through the loop clockwise. With the help of a diagram, explain how the direction of the magnetic field can be determined inside and outside the loop. Name the law used to find the direction of magnetic field.
Answer. Consider a circular loop of wire of radius r with centre O lying in the plane of the paper. Let the current i pass through the loop clockwise. According to right hand thumb rule, direction of magnetic field due to any portion of small current carrying length of the coil is:
Direction of magnetic field inside the loop — Perpendicular to the plane of paper inwards.
Direction of magnetic field outside the loop — Perpendicular to the plane of paper outwards.

So, the direction of magnetic field can be considered as the direction of total magnetic field due to circular coil as current through all the elements will contribute to the magnetic field in the same direction.

Q. 8 A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a) pushed into the coil,
(b) withdrawn from inside the coil,
(c) held stationary inside the coil?
Answer.
(a) When a bar magnet is pushed into the coil, magnetic field lines linked with
the coil changes (increases). It causes the electric current to get induced in it. The needle of galvanometer will move momentarily in one direction.
(b) When a bar magnet is withdrawn from inside the coil, the magnetic field lines linked with the coil changes but in decreasing order. Current will be induced in the coil which will be indicated by deflection of needle in the galvanometer. The deflection is opposite to that in case (a). This indicates that the direction of induced current is now opposite to the direction of induced current in case (a).
(c) When bar magnet is held stationary inside the coil, there is no deflection in the galvanometer. This is because there is no change in magnetic field lines linked with the coil. Hence, no induced current will flow through the coil.

Q.9 (a) Two magnets are lying side by side as shown below.
Draw magnetic field line between poles P and Q.

(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer.

(b) The degree of closeness of magnetic field lines near the poles signify that the field is stronger there, i.e. the pole of another magnet when placed in the magnetic field experiences a greater force where the field lines are crowded.

Q.10 For the current carrying solenoid as shown below, draw magnetic field lines and giving reason explain that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum.

Answer. Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half to that inside it. So Minimum – at point B; Maximum – at point A

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Q.1 (a) Write two points of difference between electric energy and electric power. (6) Out of 60 W and 40 W lamps, which one has higher electrical resistance when in use.
(c) What is the commercial unit of electric energy? Convert it into joules.
Answer. (a) Difference between electric energy and electric power:

i.e. less the power of electrical device, higher is its electrical resistance.
(c) Kilowatt hour – Commercial unit of electrical energy
1 kWh = 1000 Wh = 1000 J/S x 3600 sec
= 3600000 J = 3.6 x10⁶J

Q.2 V-I graph for two wires A and B are shown in the figure. If both wires are of same length and same thickness, which of the two is made of a material of high resistivity? Give justification for your answer.

Answer. Greater than slope of V-I graph, greater will be the resistance of given metallic wire. In the given graph, wire A has greater slope then B. Hence, wire A has greater resistance.
For the wires of same length and same thickness, resistance depends on the nature of material of the wire, i.e.

Q.3 An electric bulb of resistance 200Ω draws a current of 1 Ampere. Calculate the power of the bulb the potential difference at its ends and the energy in kWh consumed burning it for 5h.
Answer. Power of the bulb,

Q.4Two identical wires one of nichrome and other of copper are connected in series and a current (I) is passed through them. State the change observed in the temperatures of the two wires. Justify your answer. State the law which explains the above observation.
Answer. The resistivity of nichrome is more than that of copper so its resistance is also high. Therefore, large amount of heat is produced in the nichrome wire for the same current as compared to that of copper wire. Accordingly, more change in temperature is observed in the nichrome wire. This is explained by Joule’s law of heating.
Joule’s law of heating: It states that the amount of heat produced in a conductor is

Q.5 A 9Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination.
Answer.

Q.6 Explain the role of fuse in series with any electrical appliance in an electric circuit. Why should a fuse with defined rating for an electric circuit not be replaced by one with a larger rating?
Answer. Fuse wire is a safety device connected in series with the live wire of circuit. It has high resistivity and low melting point. It melts when a sudden urge of large current passes through it and disconnects the entire circuit from the electrical supply. But, in case if we use a larger rating instead of a defined rating, then it will not protect the circuit as high current will easily pass through it and it will not melt.

Q.7 The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating of the filament in the two cases).
Answer.

Q.8 Name the physical quantity which is (i) same (ii) different in all the bulbs
when three bulbs of:
(a) same wattage are connected in series.
(b) same wattage are connected in parallel.
(c) different wattage are connected in series.
(d) different wattage are connected in parallel.
Answer. (a) For identical bulbs in series- same current, same potential difference.
(b) For identical bulbs in parallel- same potential difference, different current.
(c) For unidentical bulbs in series- same current, different potential difference.
(d) For unidentical bulbs in parallel- different current, same potential difference.

Q.9 (a) Define the term ‘coulomb’.
(b) State the relationship between the electric current, the charge moving through a conductor and the time of flow.
Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA.
Answer.

(a) When 1 A current flows across the wire in 1 second, the charge transfer across its ends is said to be 1 coulomb.
(b) The relationship between the electric current I, the charge q and time t is

10.(a) Define the term ‘volt’.
(b) State the relation between work, charge and potential difference for an electric circuit.
Calculate the potential difference between the two terminals of a battery if 100 J of work is required to transfer 20 C of charge from one terminal of the battery to the other.
Answer.
(a) When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the electric field, then potential at that point is called 1 volt.
(b) Potential difference, V = Work done on unit charge =W/q

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Q.1 Study the diagram given below and answer the questions that follow it:

(a) Which defect of vision is represented in this case? Give reason for your answer.
(b) What could be the two causes of this defect?
(c) With the help of a diagram show how this defect can be corrected by the use of a suitable lens. [Delhi(C)]
Answer. (a) Hypermetropia as the image is formed beyond the retina.
(b) (i) Due to greater focal length of the , lens and
(ii) As eyeball becomes smaller.
(c) It can be corrected by using a convex lens of suitable focal length as shown below.

Q.2 Student sitting at the back bench in a class is not able to see what is written on the blackboard. He however, sees it clearly when sitting on the front seat at an approximate distance of 1.5 m from the blackboard. Draw ray diagrams to illustrate the image formation of the blackboard when he is seated at the (i) back seat (ii) front seat. [All India (C)]
Answer. (i) When student is seated at the back seat.

(ii) When student is seated at front seat.

Q.3 What is meant by spectrum of white light? How can we recombine the components of white light after a prism has separated them? Draw a diagram to illustrate it. [Foreign, All India (C)]
Answer. The coloured pattern VIBGYOR formed by a prism by splitting the incident white light is called a spectrum. By having two prisms, inverted to each other, one can recombine the light to get white light again.

Q.4 Explain why do the planets not twinkle but the stars twinkle. [Delhi (C); Delhi 2011]
Answer. Planets being of larger size can be taken as a collection of large number of point-sized objects/sources of light, which nullify the twinkling effect of each other.
Due to varying conditions of atmosphere, starlight undergoes multiple refraction and its path varying slightly while passing through the atmosphere. Therefore, the apparent position of star fluctuates and amount of light entering the eye changing continuously. The star sometimes appear brighter and some other time, it appears fainter. This causes twinkling of star.

Q.5 What is myopia (near-sightedness)? Draw a ray diagram to show how it can be corrected using a lens. [Delhi]
Answer. Myopia is the inability of an eye in viewing long distant objects. The image in this case is formed before the retina. For every myopic eye, there exists a far point beyond which clear image cannot be seen.
The short-sightedness is corrected by using a concave lens which diverges and shifts the image to the retina.

Q.6 What is hypermetropia (far-sighted-ness)? Draw a ray diagram to show how this defect can be corrected using a lens. [Delhi]
Answer. Hypermetropia is the inability of an eye in viewing the nearby objects. The image in this case is formed beyond the retina. For a hypermetropic eye, there exists a near point.
It is corrected by using a convex lens, which converges and shifts the image to the retina.

Q.7 What is a spectrum? Why do different coloured rays deviate differently on passing through a glass prism? [All India]
Answer. The band of coloured component of a light beam is called its spectrum. The colour sequence is given by the acronym V I B G Y O R — Violet, Indigo, Blue, Green, Yellow, Orange and Red.
The speed of light of different colours in a medium like glass is different. Varying speeds for different colours lead to different refractive indices for different colours. It has been observed that the refractive index of glass for violet colour is more than that for red colour. All the colours present in white light refract through different angles and hence, emerge out from the prism with different directions and become distinct.

Q.8 What is meant by the term ‘power of accommodation’ of human eye? How does it help a person to see nearby as well as distant objects clearly.[Foreign]
Answer. The ability of eye lens to adjust its focal length to form the sharp image of the object at varying distances on the retina is called its power of accommodation.
When we see the nearby object, the ciliary muscles contract, it increases the thickness of eye lens. The eye lens then becomes thicker. As a result, the focal length of eye lens decreases in such a way that the clear sharp image of nearby object is formed on the retina. Thus, the object is seen clearly to us.
When we see the distant object, these muscles becomes relaxed, thus the eye lens becomes thinner, and consequently focal length of the lens increases. Therefore, the parallel rays coming from the distant object are focused on the retina and object is seen clearly to us. Thus, the accommodation power of an eye helps a person to see nearby as well as distant objects clearly

Q.9 a) Explain the following terms used in relation to defects in vision and correction provided by them:
(i) Myopia (ii) Astigmatism (iii) Bifocal lenses (iv) Far-sightedness.
(b) Why is the normal eye unable to focus on an object placed within 10 cm from the eye? [All India]
Answer. (a) (i) Myopia: Short-sightedness is caused due to excessive curvature in cornea or elongation of eyeball. Image is formed before of the retina. So, a concave lens is used to correct it.
(ii) Astigmatism: The inability to focus the light in both vertical and horizontal lines is called astigmatism. It is caused due to varying curvature in lens both horizontally and vertically. It is . corrected by using cylindrical lens.
(iii) Bifocal lenses: These are used to correct presbyopic eye. These contain lenses with upper concave and lower convex surface. Presbyopia arises with age.
(iv) Far-sightedness: Hypermetropia or far-sightedness is caused due to greater focal length of eye lens and/or when eyeball becomes smaller. Image is formed beyond the retina and can be corrected using a convex lens.
(b) The focal length of the lens cannot be changed up to an extent that objects nearer than 25 cm can be viewed (its near point is 25 cm). So it is not able to focus for 10 cm.

Q10.A 14-year old student is not able to see clearly the questions written on the blackboard placed at a distance of 5 m from him.
(a) Name the defect of vision he is suffering from.
(b) With the help of labelled ray diagrams show how this defect can be corrected.
(c) Name the type of lens used to correct this defect. [All India]
Answer.

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Question 1.
How does investment in human capital yield a return just like investment in physical capital?
Answer:
(i) Investment in human capital (through education, training, medical care) yields a return just like investment in physical capital. This can be seen directly in the form of higher incomes earned because of higher productivity of the more educated or the better trained persons, as well as the higher productivity of healthier people,

(ii) Not only do the more educated and the healthier people gain through higher incomes, society gains also in other indirect ways because the advantages of a more educated or a healthier population spreads to those also who themselves were not directly educated or given health care. In fact, human capital is in one way superior to other resources like land and physical capital. Human resource can make use of land and capital. Land and capital cannot become useful on its own.

Question 2.
What different the strategies should be made by the government to solve the unemployment in India.
Answer:
The strategies made by the government to solve the problem of unemployment in India:

• Heavy Investment in Basic Industries: Investment in heavy and basic industries and consumer goods industries should be increased. They provide more employment along with the supply of consumer goods.
• Development of Cottage and Small-scale Industries: They provide more employment by adopting labour intensive techniques.
• Change in Educational System: More emphasis should be given to vocational education.
• Checking of Population Explosion: Rapidly rising population should be checked by adopting family planning and welfare schemes.
• Modernisation of Agriculture: Modernisation of agriculture should be done. Waste lands should be utilised.
• Introduction of Rural Works Programmes: Rural works programmes should be increased.
• Developing Infrastructure of Economy: Infrastructure of the economy should be developed.
• Subsidies to Private Sector: Subsidies and other incentives should be given to private sector.
• Stress on Self-employment: Young entrepreneurs should be encouraged for sell-employment by giving proper training and financial assistance.

Question 3.
What is an economic activity ? What cue various activities undertaken in the primary sector, secondary sector and tertiary sector ?
Answer:
Economic activities: All the activities which give us some income are called economic activities. Pulling cycle-rickshaw, cleaning houses, selling vegetables and working in schools, factories, banks, etc. are economic activities.
Activities undertaken in Primary, Secondary and Tertiary Sectors are :

• Primary Sector: Activities concerned with collecting or making available material provided by nature are included in primary sector like agriculture, poultry farming, mining, fishing, etc.
• Secondary Sector: The activities which are associated with transforming raw material or primary products into commodities useful to man such as manufacturing, etc.
• Tertiary Sector: The activities which are essential for running modern factories in a big way are termed as tertiary sector. Activities like trading, banking, health, education, insurance, etc. are included in tertiary sector and all there providing services.

Question 4.
What are the different types of unemployment found in India?
Answer:
The different types of unemployment found in India are :

• Disguised unemployment: In disguised unemployment, people appear to be employed. They have agricultural plot where they find work. This usually happens among family members engaged in agricultural activity.
• Seasonal unemployment: Seasonal unemployment happens when people are not able to find jobs during some months of the year. People dependant upon agriculture usually face such ldnd of problem. There are certain busy seasons when sowing, harvesting, weeding and threshing is done. Certain months do not provide much work to the people dependent on agriculture.
• Educated unemployment: Educated unemployment has become a common phenomenon in urban areas. Many youths with matriculation, graduation and post-graduation degrees are not able to find job. A study showed that unemployment of graduate and post-graduate has increased faster than among matriculates.

Question 5.
How does Sarva Siksha Abhiyan help in improving elementary education in India?
Answer:
Sarva Siksha Abhiyan is a significant step towards providing elementary education to all children in the age group of 6-14 years by 2010. It is a time-bound initiative of the Central Government, in partnership with the States, the local government and the community for achieving the goal of universalisation of elementary education.

Along with it, bridge courses and back-to-school camps have been initiated to increase the enrolment in elementary education. Mid-day meal scheme has been implemented to encourage attendance and retention of children and improve their nutritional status. It is because of Sarva Siksha Abhiyan that there has been a significant growth in literacy \ rates in India from 18% in 1951 to 74% in 2010-11. These policies have added to the literate population of India.

Suggest any three ways to transform population load into an asset.
Answer:
The three ways to transform population load into an asset are :

• To improve literacy rate: Education provides new aspiration and develops values of life. Education helps in enhancing the national income, cultural richness and increases the efficiency of governance.
• Health: The health of a person helps him to realise his potential and the ability to fight illness. Increase in longevity of life in an indicator of good quality of life marked by self-confidence. It involves the protection of children from infection, ensuring nutrition and along with mother and the child and child care.
• Formation of skills: Providing vocational and skill-based education helps the people to get employment and therefore, they contribute to the national income later.

Question 6.
What is the nature of unemployment in India?
Answer:
In India, unemployment is widespread. Unemployment is found both in its rural and urban areas. There is seasonal and disguised unemployment in its rural areas. People here are dependent on agriculture. Certain months do not provide much work to the people dependant upon agriculture.

In urban areas, educated unemployment has become a serious problem. Many educated youths are not able to find jobs. Unemployment among graduates and post-graduates has increased f§ster than among the matriculates.

Question 7.
What measures have been taken by the government to spread education and skills among boys and girls ?
Answer:
There is a provision made for providing universal access, retention and quality in elementary education with a special emphasis on girls. There is also an establishment of pace setting of schools like Navodaya Vidyalaya in each district. Vocational streams have been developed to equip large number of high school students with occupations related to knowledge and skills.

Question 8
What are the objectives of the 12th Five Year Plan in the field of education?
Answer:
The 12th plan endeavoured to raise the country’s Gross Enrolment Ratio (GER) in higher education in the age group of 18 to 23 years to 25.2% by 2017-18 and to reach the target of 30% by 2020-21, which would be broadly in line with world average. The strategy focuses on increasing access, quality, adoption of state-specific curriculum modification, vocationalisation and networking on the use of information technology. The plan also focuses on distance education, convergence of formal, non-formal, distance and IT education institutions.

Question .9
What are the measures taken by the government to improve literacy conditions in India?
Answer:
The following the measures have been taken by the government to improve literacy conditions in India

• Opening of Navodaya Vidyalayas: Government has started to establish Navodaya Vidyalayas in each district. Vocational streams have been developed to equip large number of high school students with occupations related to knowledge and skills.
• Sarva Siksha Abhiyan: It is a significant step towards providing elementary education to all the children of age group 6-14 years. It is an initiative of the Central Government in partnership with the States, the local government and the community for achieving the goal of universalisation of elementary education.
• Mid-day Meal Scheme: It is a programme aimed to encourage attendance and retention of children in schools and improve their nutritional status.

Question 10
Why did Japan emerge as a developed country inspite of its poor natural resource?
Answer:
Japan emerged as a developed country inspite of its poor natural resource because :

• As they did not have any other resource they invested in the development of human resource.
• They import the natural resource needed in their country. They have invested on people, especially in the field of education and health.
• These people have made efficient use of other resources, like land and capital. Efficiency and the technology evolved by people have made these countries rich and developed.



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Q.1 What is ‘reproduction’? Mention the importance of DNA copying in reproduction.
Answer. Reproduction is the process of producing new individuals of the same species
by existing organisms of a species, i.e. parents. The importance of DNA copying in reproduction are as follows:
(i) DNA copying is called DNA replication. In this process, one copy each of replicated DNA will be passed to daughter cells.
(ii) Variations may be introduced during DNA copying. This inbuilt tendency for variation during reproduction forms the basis of evolution.

Q.2 “Variations that confer an advantage to
an individual organism only will survive in a population.” Justify.
Answer. It is because the chances of survival depend on the nature of variations and different individuals have different kinds of advantages.
For example, a bacteria that can withstand heat will survive better in a heat wave, i.e. the organisms that are fit in the competitive environment and with great variations will be able to survive and adapt. Thus, more off springs and population with genetic variations will survive.

Q.3 (a) In the human body what is the role of
(i) seminal vesicles, and (ii) prostate gland?
(b) List two functions performed by testis in human beings.
Answer. (a) The role of seminal vesicles and the prostate gland are as follows:
(i) Seminal vesicles produce seminal plasma which is in the form of fluid makes the transport of sperms smooth.
(ii) Prostate gland secretes prostatic fluid that keeps the sperms alive and helps them to swim vigorously.
(b) Two functions performed by testis
in human beings are as follows:
(i) Formation of sperms takes place in testis.
(ii) They secrete the hormone testosterone which regulates the formation of sperms and brings changes in appearance of boys at the time of puberty.

Q 4. Illustrate the following with the help of suitable diagrams:
(i) Regeneration in Planaria.
(ii) Budding in Hydra.
Answer.

Q.5 Illustrate the following with the help of suitable diagrams:
(i) Binary Fission in Amoeba.
(ii)Leaf of Bryophyllum with buds.
Answer.

Q 6. Write the full form of DNA. Name the part of the cell where it is located. Explain its role in the process of reproduction of the cell.
Answer. The full form of DNA is deoxyribonucleic acid. It is the genetic material found in the chromosomes, which are present in the nucleus of a cell.
Role of DNA in the process of reproduction of the cell:

DNA plays an important role in the reproduction of a cell. The reproducing cell produces an identical copy of DNA through some cellular mechanism. Since the newly formed copy of DNA lacks an organised cellular structure, the cell gets divided to provide cell cover to the newly formed DNA. Thus, two daughter cells are formed from the single cell as a result of the copying of DNA.

.

Q.7  List any three differences between pollination and fertilisation.
Answer.

Q.8 Draw a longitudinal section of a flower and label the following parts:
(i) Part that produces pollen grain.
(ii)Part that transfers male gametes to the female gametes.
(iii) Part that is sticky to trap the pollen grain.
(iv) Part that develops into a fruit.
Answer.

Q.9 Explain the following methods of contraception giving one example of each:
(i) Barrier method
(ii) Hormonal imbalance method
Answer.
(i) Barrier Method: In this method, physical devices such as condoms, diaphragm and cervical caps are used. These devices prevent the entry of sperm in the female genital tract during copulation, thus acting ‘ as a barrier between them.
(ii) Hormonal Imbalance Method: In
this method, specific drugs are used by females, which are of two types: oral pills and vaginal pills.
Oral pills contain hormones which stop the ovaries from releasing ovum into the fallopian tube. These pills are also called oral contraceptives (OCs) which act by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur. The use of Intrauterine Contraceptive Devices (IUCDs) prevents implantation in the uterus. This device is copper-T placed safely inside the uterus by a doctor or nurse.

Q.10 (a) What is spore formation?
(b) Draw a diagram showing spore formation in Rhizopus.
(c) List two advantages for organisms
to reproduce themselves through spores.
Answer.

(a) When a slice of bread is kept in moist dark place for a few days, spores of Rhizopus present in air settle on the bread to form new fungus plants of Rhizopus.
(b) The Rhizopus consists of fine thread-like projections called hyphae. It has a knob like structure which is involved in reproduction called sporangia, containing spores, that develop into new Rhizopus.

c) Two advantages for organisms to reproduce themselves through spores are as follows:
(i) It is a faster mode of reproduc-tion.
(ii) Offsprings produced are identical.

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Q.1 What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
Answer. Speciation is the evolution of reproductive isolation among once interbreeding population.
Factors which can lead to speciation are:

1. Genetic drift: Over generations, genetic drift may accumulate which leads to speciation.
2. Natural selection: Natural selection may work differently in different location which may give rise to speciation.
3.  Severe DNA change.
4. A variation may occur which does not allow sexual act between two groups.

Q.2 What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why? [All India]
Answer. Homologous organs are those organs which have the same basic structural design and developmental origin but have different functions and appearance.
Example: The forelimb of a frog, a lizard, a bird and a man seem to be built from the same basic design of bones, but they perform different functions.

Q.3 Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited? [Delhi(C)]
Answer. Acquired trait is a particular characteristic that is developed during the lifetime of an individual. Such characteristics are not genetically controlled and cannot be passed on to the next generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs, generation to generation. Such traits are genetically determined characteristic that distinguishes a person.
Example: Colour of skin.
The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.

Q.4 Define ‘evolution’. Describe Darwin’s theory of evolution. [All India]
Answer. Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years and new species are produced. Since, the evolution is of the living organisms, so it is called ‘Organic Evolution’.
Darwin’s theory of Evolution: Charles Robert Darwin gave the theory of evolution in his famous book, ‘The Origin of Species’. The theory of evolution proposed by Darwin is known as ‘The Theory of Natural Selection’. It is also called ‘Darwinism’.
According to Darwin’s theory of evolution:

1. There is natural variation within any population and some individuals have more favourable variations than others.
2. Population remains fairly constant even though all species produce a large number of off springs.
3. This is due to ‘competition’ or struggle for existence between same and different species.
4. The struggle for survival within population eliminates the unfit individuals and those with ‘favourable variations’ survive and pass on these variations to their progeny to continue. This is called natural selection.
5. The favourable variations are accumulated over a long time period leading to the origin of a new species.

Q.5 Define variation in relation to a species. Why is variation beneficial to the species? [Delhi]
Answer. Variation refers to the differences in the characters or traits among the individuals of a species.
Variations are beneficial to the species because:

1. They enable the organisms to adapt themselves in changing environment.
2. Variations form the basis of heredity.
3. They form the raw materials for evolution and development of new species.

Q.6. Explain the terms: (i) Speciation (ii) Natural selection [Delhi]
Answer. (i) Speciation is the evolution of reproductive isolation among once-interbreeding populations, i.e. the development of one or more species from an existing species.
(ii) Natural selection is the process, according to Darwin, which brings about the evolution of new species of animals and plants.

Q7. Explain with examples how the following are evidences in favour of evolution in organisms. (i) Homologous organs (ii) Analogous organs (iii) Fossils [Delhi]
Answer. (i) Forelimb of human and bird are homologous organs. They have same structural design and developmental origin but they have different functions and appearance. Homologous organs help us to understand that the organism has evolved from a common ancestor. The more common characteristics the two species have, the more closely they are related.
(ii) Analogous organs are those organs design and developmental origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. They have a common function of flying but their origins are not common. So, birds and bats are not closely related.
(iii) Fossils and their study is useful in knowing about the species which are no longer alive. They provide evidence and missing links between two classes. They are helpful in forming a sequence of organisms in the pathway of evolution. Thus, fossils have an importance in deciding evolutionary relationship. Archaeopteryx is a fossil bird. It had feathers, fused bones and beak which are exclusively bird structures. It also had some features which are found in reptiles, e.g. teeth in jaw, claws on free fingers and a long tail. This fossil provides a clue that birds have evolved from reptiles.

Q.8 State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Answer. Inherited traits are the characteristics transmitted from parents to their off spring. Acquired traits are characteristics which are developed during the lifetime of an individual. Acquired traits are not passed on to the next generation. For example, if we breed a group of mice, all their progeny will have tails. Now, if the tails of these mice are removed by surgery and allowed to breed, the next generation mice will also have tails. If these tails are also removed and allowed to breed, the progeny of mice will again have tails. Removal of tail by surgery is an acquired trait and do not change the genes of germ cells and hence, are not passed on to the next generation.

Q.9 What are fossils? What do they tell us about the process of evolution?
Answer. The remains of dead plants and animals which were buried under the rocks millions of years ago are called fossils.
Fossils tell us about the process of evolution. The fossils of different organisms have some features similar to one species while some features are similar to the other species. In this way, they show the link between two species. They tell us that one species evolves from the other.

Q.10 The human beings who look so different from each other in terms of colour, size and looks are said to belong to the same species. Why? Justify your answer. [All India(C)]
Answer. Human beings are said to belong to the same species because of the following reasons:

1. DNA studies.
2. Number of chromosome is same,
3. All have a common ancestor.
4. They interbreed among themselves to produce fertile young ones of their own kind.

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Q 1.In single celled organisms diffusion is sufficient to meet all their requirements of food, exchange of gases or removal of wastes but it is not in case of multicellular organisms. Explain the reason for this difference.
Answer. Unicellular organisms can absorb sufficient oxygen because of its complete contact with the atmosphere, but in multicellular organisms the rate of absorption and diffusion becomes very less because all cells are not in direct contact with the atmosphere. Multicellular organisms require greater amount of oxygen to sustain life processes which cannot be fulfilled by the process of diffusion.

Q 2. Draw a diagram of human excretory system and label kidneys, ureters on it.
Answer.

Q 3..Name the acid presents in the following:
(i) Tomato (ii) Vinegar (iii) Tamarind
Answer.
(i) Oxalic acid (ii) citric acid (iii) Tartaric acid.

Q 4.State the role of the following in human digestive system :
(i) Digestive enzymes (ii) Hydrochloric acid (iii) Villi
Answer.
(i) Digestive enzymes – Foods need to be broken into their small or simpler
molecules so that they can be absorbed into the bloodstream. However, the physical breakdown of food is not enough. Enzymes are hence needed for the chemical breakdown of food and speeding up the digestive process. The products of digestion can hence be small enough to be absorbed.
(ii) Hydrochloric acid – Hydro chloric acid helps to kill the germs which might have entered in to the system through food. It creates acidic medium for the pepsin to act on food to breakdown proteins.
(iii) Villi – Villi are finger like projections in the small intestine. They help to increase the surface area for absorption of the digested food. Villi are richly supplied with blood vessel which help to absorb digested food in to the blood stream..
Q 5.(a) Name the site of exchange of material between the blood and surrounding cells. (b) Draw a schematic representation of transport and exchange of oxygen and carbon dioxide in human body.
Answer.
(a) Capillaries
(b)

Q 6.What would be the consequences of deficiency of hemoglobin in your body?
Answer. The deficiency of hemoglobin in our body is called anemia. In anemia, the blood is unable to carry the sufficient amount of oxygen required by the body. So, respiration would be less and less energy will be available to the body. The hemoglobin deficient person will feel weak, pale, lethargic and will be
unable to perform heavy physical work.

Q 7. List three characteristics of lungs which make it an efficient respiratory surface.
Answer. These features which particularly make our lungs efficient for gas exchange.
1.Thin: the air sac walls are very thin so that gases can quickly diffuse through them. Oxygen is absorbed in to the blood and carbon dioxide is given out in to the lungs to be exhaled out.
2.Moist: the air sacs are moist with mucus so that gases can dissolve before diffusing.
3.Large surface area: the surface area for gases to diffuse through in human lungs is roughly the same as a tennis court. The alveoli help to increase the surface area for absorption of oxygen.
4.Good blood supply: the air sacs or the alveoli have a large capillary network so that large volumes of gases can be exchanged. More the flow of blood more exchange.

Q 8.(a) Draw a diagram of human respiratory system and label the following:
(i) part where air is filtered by fine hair and mucus
(ii) part which terminates in balloon – like structures
(iii) balloon – like structures where exchange of gases takes place. (iv) part which separates chest cavity from abdominal cavity.
(b) Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?
Answer.(a)

(b) Quantity of dissolved oxygen is fairly low in water as compared to the amount of oxygen in air. Aquatic organisms therefore have to breath faster than terrestrial organisms to absorb the required amount of oxygen from the water.

Q 9.(a) What is the role of HCl in our stomach ?
(b) What is emulsification of fats ?
(c) Which protein digesting enzyme is present in pancreatic juice ?
Answer.
(a)(i) It sterilises food by killing pathogens and other microbes.
(ii) It has a pH of 2, which is perfect for entyaus such as pepsin to break down proteins as effectively as possible.
(iii) Helps emulsify food (digestion of protein and stimulates the pancreas to produce digestive enzymes and bile) and protects against harmful ‘ bacteria
(b) Breakdown of large gloubule fats into smaller fats droplets is known as emulsification.
(c) Trypsin is the enzyme secreted by the pancreas which aids in digestion of proteins.

Q.10 Draw a diagram of human excretory system and label renal artery and urethra.
State in brief the function of :

1. renal artery
2.  kidney
3.  ureter
4. urinary bladder

Answer.

1. Renal artery: The renal artery carries blood to the kidneys from the abdominal aorta. This blood comes directly from the heart and is sent to the-kidneys to be filtered before it passes through the rest of the body. Up to one-third of the total cardiac output per heartbeat is sent to the renal arteries to be filtered by the kidneys. Each kidney has one renal artery that supplies it with blood. The filtered blood then can exit the renal vein.
2. Kidney: The kidneys perform the essential function of removing waste products from the blood and regulating the water fluid levels. The kidneys regulate the body’s fluid volume, mineral composition and acidity by excreting and reabsorbing water and inorganic electrolytes.
3. Ureter: The ureter is a tube that carries urine from the kidney to the urinary bladder.’ There are two ureters, one attached to each kidney.
4. Urinary bladder: The urinary bladder is an expandable muscular sac that stores urine before it is excreted out of the body through the urethra.

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Q1.Giving reasons, explain the following:
(a) Element A is a non-metal.
(b) Element B has a larger atomic size than element C.
(c) Element C has a valency of 1
Answer. (a) ‘A’ is non-metal because it can gain electron easily as it has 7 valence electrons and forms negative ion with stable electronic configuration.
(b) It is because ‘B’ has lesser atomic number, less nuclear charge, less force of attraction between valence electrons and nucleus therefore, has larger atomic size.
(c) ‘C’ has 7 valence electrons. It can gain one electron to become stable. So, its valency is equal to one

Q 2. In the following table, six elements A, B, C, D, E and F (here letters are not the usual symbols of the elements) of the Modern Periodic Table with atomic numbers 3 to 18 are given:

(a) Which of these halogen ?is (i) a noble gas, (ii) a halogen
(b) If B combines with F, what would be the formula of the compound formed?
(c)Write the electronic configurations of C and E.
Answer.

Q 3. In the following table, are given eight elements A, B, C, D, E, F, G and H (here letters are not the usual symbols of the elements) of the Modern Periodic Table with the atomic numbers of the elements in parenthesis.

1.  What is the electronic configuration of F?
2. What is the number of valence electrons in the atom of F?
3. What is the number of shells in the atom of F?
4.  Write the size of the atoms of E, F, G and H in decreasing order,
5.  State whether F is a metal or a non-metal.
6. Out of the three elements B, E and F, which one has the biggest atomic size?

Answer.

1.  F has electronic configuration 2, 8, 2.
2.  F has 2 valence electrons.
3. There are three shells in ‘F’.
4.  H > G > F > E is decreasing order of size of atbms.
5.  ‘F’ is a metal.
6. ‘B’ is having biggest atomic size among B, E and F.

Q 4. How can the valency of an element  be determined if its electronic
configuration is known? What will be ‘ the valency of an element of atomic number 9 (nine)?
Answer. If the element has 1, 2, 3, 4 valence electrons, its valency will be 1, 2, 3, 4
respectively. If the element has 5, 6, 7, 8 valence electrons, its valency will be 3, 2, 1, 0. Element with atomic number 9 has electronic configuration 2, 7. So, its valency will be 1.

Q 5. How does the electronic configuration of an atom of an element relate to its position in the modern periodic table? Explain with one example.
Answer. The position of element depends upon number of valence electrons which depend upon electronic configuration. Those elements which have same valence electrons, occupy same group.
Those elements which have one valence electron belong to group 1.
Elements with two valence electrons belong to group 2.
Period number is equal to number of shells.
If valence electrons are equal to 1, it belongs to group 1. If it has 2 shells, it belongs to second period, e.g. if element ‘X’ has atomic number 11, its electronic configuration is 2, 8,1. It has one valence electron, it belongs to group 1 and it has three shells therefore, it is in third period.

Q 6. The atomic number of an element is 16. Predict

1.  the number of valence electrons in its atom
2. its valency
3. its group number
4. whether it is a metal or a non- metal
5.  the nature of oxide formed by it
6. the formula of its chloride

Answer. The electronic configuration of S(16) is 2, 8, 6.

1.  6
2. 2
3. 16
4.  Non-metal
5.  Acidic oxide
6. SCl₂is a formula of its chloride.

Q 7. (a) did Mendeleev have gaps in his periodic table?
(b) any three limitations of Mendeleev’s classification.
(c) does electronic configurations of atoms change in a period with increase in atomic number?
Answer.(a)Gaps were left for undiscovered elements in the Mendeleev’s Periodic Table.
(b)(i) Position of hydrogen was not justified.
(ii)Increasing order of atomic mass could not be maintained.
(iii) Isotopes have similar chemical properties but different atomic masses, they cannot be given separate places.
(c)Number of shells remains the same, number of valence electrons goes on increasing
from left to right in a period till octet is comilete,e.g.

Q.8 In the modern periodic table, the element Calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these elements has physical and chemical properties resembling those of Calcium and why?
Answer. Elements with atomic number 12, 38 resemble calcium in physical and chemical properties because they have same number of valence electrons and belong to same group 2.
Mg(12) : 2, 8, 2
Ca(20) : 2, 8, 8, 2
Sr(38) : 2, 8, 18, 8, 2 Q.9 The atomic numbers of three elements, X, Y and Z are 9,11 and 17 respectively. Which two of these elements will show similar chemical properties? Why?
Answer. Electronic configuration of X, Y and Z will be:
X(9) : 2, 7
Y(11) : 2, 8, 1
Z(17) : 2, 8, 7
X and Z will show similar chemical properties due to same number of valence electrons
Q 10. An element ‘X’ belongs to 3rd period and group 17 of the periodic table. State its (a) electronic configuration, (b) valency. Justify your answer with reasoning.
Answer.
(a) X(17) : 2, 8, 7
(b) Valency : 1
It has atomic number 17 and therefore, electronic configuration will be 2, 8, 7. It can gain one electron to become stable therefore, its valency is equal to 1. It belongs to third period, as it has three shells. It belongs to group 17 because it has 7 valence electrons

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1. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?

(b) Write a balanced chemical equation for the reaction taking place.
Answer

(a)
(i) There will be no action on dry litmus paper.

(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.
(b) S (s) + O₂(g) → SO₂ (g)

2.State two ways to prevent the rusting of iron.

Answer

Two ways to prevent the rusting of iron are:
→ Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
→ Galvanisation:An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.

3. Differentiate between metal and non-metal on the basis of their chemical properties.

Answer

Metal	Non-metal
Metals are electropositive.	Non-metals are electronegative.
Oxides of metal are basic in nature.	Oxides of non-metals are acidic in nature.
Metals displace hydrogen from dilute acids.	They can’t replace hydrogen from dilute acids.
Metals form chlorides which are electrovalent or ionic compounds.	Non-metals form chlorides which are covalent compounds.
They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam.	They do not react with water.

4. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na₂O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?

Answer

(i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure for elements.

(ii)

(iii) The ions present in Na₂O are Na⁺ and O^2– ions and in MgO are Mg²⁺ and O^2– ions.

5. (a) Write electron dot diagram for chlorine (At No. 17) and calcium (At No. 20).
Show the formation of calcium chloride by transfer of electrons.
(b) Identify the nature of above compound’and explain three physical properties of such compound. Answer.

(b) It is ionic compound.
Physical properties
1.It is hard and solid.
2.It has high melting and boiling point.
3.It soluble in water.

6. (a) An ore on treatment with dilute hydrochloric acid produces brisk effervesces. What type of ore is this? What steps will be required to obtain metal from the enriched ore. ,
(b) Copper coin is kept immersed in silver nitrate solution for some time. What change will take place in coin and colour of the solution ? Write balanced chemical equation of the reaction involved.
Answer.
(a) Carbonate ore:
(i) Calcination: Carbonate ore is heated in limited supply of air and oxide is obtained, e.g.

(b) Copper, being more reactive than silver will displace silver from silver nitrate solution and there will be deposition of silver on copper coin. The colour of solution will turn to blue.

7.(a) Define activity series of metals. Arrange the metals gold, copper, iron and magnesium in order of their increase in reactivity.
(b) What will you observe when:
(i) Some zinc pieces are put in copper sulphate solution.
(ii) Some silver pieces are put into green coloured ferrous sulphate solution.
Answer.
(a) The series of metals in which metals are arranged in decreasing order of their reactivity.
Au < Cu < Fe < Mg is increasing order of reactivity.
(b) (i) The blue solution will become colourless and reddish brown copper metal will be deposited.

Reaction will not take place because Ag’ is less reactive than iron.

 8.Give reason for the following:
(a) Aluminium oxide is considered as an amphoteric oxide.
(b) Ionic compounds conduct electricity in molten state.
Answer.
(a) It is because it reacts with acids as well as bases to produce salts and water.’Al’ is less electropositive metal. So, it forms amphoteric oxide which can react with acid as well as base.
(b) Ionic compounds can conduct electricity in molten state because ions ’ become free to move in molten state.

9.Write balanced equations for the reaction of:
(i) aluminium when heated in air. Write the name of the product.
(ii) iron with steam. Name the product obtained.
(iii) calcium with water. Why does calcium start floating in water?
Answer.

The bubbles of hydrogen stick to the surface of metal that is why it floats.

10. What is meant by ‘rusting’? With labelled diagrams, describe an activity to find out the conditions under which iron rusts.
Answer. The process in which iron reacts with oxygen in the presence of moisture to form reddish brown coating of hydrated ferric oxide [Iron (III) oxide].Fe2O₃ xH₂0
Activity:
(i) Take three boiling tubes A, B and C.
(ii) Pour some water in test tube A Put iron nails in it and cork it.
(iii) Pour boiled distilled water in another test tube B and put iron nails in it. Add 1 ml of ojl over it such that oil flo’ats over it and prevents the air from entering.
(iv) Take some iron nails in test tube C and put some anhydrous calcium chloride in it and cork it.
(v) Leave all the three test tubes for one day and then observe.

Observation: Iron nails get rusted in test tube A because both air and water are present in it. Iron nails do not get rusted in B because there is water but no air. In C, rusting will not take place because there is neither air nor water. Conclusion: Iron gets rusted in the presence of air and water.

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