Here students can get info about NCERT Important Questions & MCQs for Class 6 Science so that they can get to know the answers to the questions in case they are not able to find it. You can find the best Class 6th Science NCERT Solutions explained in conformance with the CBSE curriculum for Class 6.
Table of Contents
Chapter 6 Changes Around Us Class 6th Science
MCQs
Question 1.
When ice melts into water, what types of changes do you observe ?
(a) Physical changes
(b) Chemical changes
(c) Both (a) and (b)
(d) None of these
Answer
(a) Physical changes
Ice melts into water is physical change.
Question 2.
Cooked food is the:
(a) Chemical change
(b) Physical change
(c) Both (a) and (b)
(d) None of these
Answer
(a) Chemical change
Cooked food is a chemical change.
Question 3.
If we burn a candle, the height of a candle will .
(a) Decreased
(b) Increased
(c) Remain same
(d) None of these
Answer
(a) Decreased
The height of burning candle is always decreased.
Question 4.
For making the curd, we should the milk.
(a) Heat
(b) Cool
(c) Boil
(d) None of these
Answer
(a) Heat
For making the curd, we should heat the milk.
Question 5.
Metal rim is made slightly than the wooden wheel.
(a) Bigger
(b) Smaller
(c) Equal
(d) None of these
Answer
(b) Smaller
Metal rim is made slightly smaller than the wooden wheel.
Question 6.
the metal rim expands and fits into the wheel.
(a) On boiling
(b) On cooling
(c) On heating
(d) All of these
Answer
(c) On heating
The incense stick has burnt to give off gases and ashes.
Question 7.
The black material (tar) for repairing road is .
(a) Heated
(b) Cooled
(c) Heated and cooled
(d) None of these
Answer
(a) Heated
The black material (tar) for repairing road is heated.
Question 8.
The incense stick has burnt to give off.
(a) Gases
(b) Ashes
(c) Both (a) and (b)
(d) None of these
Answer
(c) Both (a) and (b)
The incense stick has burnt to give off gases and ashes.
Question 9.
Metal expand on heating and contract on.
(a) Boiling
(b) Washing
(c) Cooling
(d) Both (a) and (b)
Answer
(c) Cooling
Metal contract on cooling.
Question 10.
A change in a substance can be brought by heating it or by it with other substances.
(a) Cooling
(b) Boiling
(c) Washing
(d) Mixing
Answer
(d) Mixing
A change be in a substance can be brought by heating it or by mixing it with other substances.
Question 11.
An iron piece is heated red hot and beaten into a shape.
(a) Desired
(b) Undesired
(c) Same
(d) All of these
Answer
(a) Desired
A iron piece is heated red hot and beaten into a desired shape.
Question 12.
The change which can be reversed is known as:
(a) Reversible change
(b) Irreversible change
(c) Both (a) and (b)
(d) None of these
Answer
(a) Reversible change
The change which can be reversed is known as reversible change.
Question 13.
The change which cannot be reversed is known as:
(a) Reversible change
(b) Irreversible change
(c) Both (a) and (b)
(d) None of these
Answer
(b) Irreversible change
The change which cannot be reversed is known as irreversible change.
Question 14.
A process in which liquid changes into gas is known as:
(a) Solution
(b) Fusion
(c) Condensation
(d) Evaporation
Answer
(d) Evaporation
Evaporation is the process in which liquid changes into gas.
Question 15.
A process by which gas is turned into liquid is known as:
(a) Solution
(b) Fusion
(c) Condensation
(d) Evaporation
Answer
(c) Condensation
Condensation is the process by which gas is turned into liquid.
Question 16.
A process in which liquid is freezed into solid is known as:
(a) Condensation
(b) Fusion
(c) Solution
(d) Evaporation
Answer
(b) Fusion
Fusion is the process in which liquid is freezed into solid.
Question 17.
When a solid dissolves in liquid then is formed.
(a) Condensation
(b) Fusion
(c) Solution
(d) Evaporation
Answer
(c) Solution
When a solid dissolves in liquid then solution is formed.
Question 18.
Write a few changes taking place around us on their own:
(a) Grain to its flour
(b) Bud to flower
(c) Cow dung to biogas
(d) Both (b) and (c)
Answer
(d) Both (b) and (c)
Bud to flower, cow dung to biogas are the changes taking place around us on their own.
Question 19.
The changes that require long time to occur are called:
(a) Fast change
(b) Slow change
(c) Permanent change
(d) Temporary change
Answer
(b) Slow change
The changes that require long time to occur are called slow change.
Question 20.
The changes which occur immediately are called:
(a) Slow change
(b) Temporary change
(c) Permanent change
(d) Fast change
Answer
(d) Fast change
The changes which occur immediately are called fast change.
Important Questions
Question 1.
What are reversible and irreversible changes?
Answer:
Reversible and irreversible changes:
Reversible changes: The changes which can be brought back to its original form are known as reversible changes. For example, melting of wax and stretching of a rubber band.
Irreversible changes: The changes in which the matter cannot be brought back to its original state are known as irreversible changes. For example, burning of paper changes it into ash and smoke. Paper cannot be obtained back from ash and smoke.
Question 2.
What are the differences between reversible changes and irreversible changes?
Answer:
The differences between reversible changes and irreversible changes:
| Reversible changes | Irreversible changes |
| 1. A change which can be undone or reversed.
2. It is a temporary change. 3. Melting and folding are examples of it. | 1. A change which cannot be undone or reversed.
2. It is a permanent change. 3. Burning and cooking of food are examples of it. |
Question 3.
Can you obtain wood from sawdust?
Answer:
No, because it is an irreversible change.
Question 4.
Can we say that ironing of a cloth is a reversible change? Give reasons.
Answer:
Ironing removes the wrinkles of the clothes, which can come back in the same condition. Hence, ironing of a cloth is a reversible change.
Question 5.
Can deforestation be considered as a reversible change?
Answer:
No, deforestation can’t be considered as a reversible change because no same tree can be planted after felling down or cutting.
Question 6.
Is printing a reversible or an irreversible change?
Answer:
Printing is an irreversible change because we cannot separate and collect the printing ink after printing.
Question 7.
Give two examples each of reversible and irreversible changes.
Answer:
Reversible changes: Melting of wax and stretching of a rubber band.
Irreversible changes: Burning of a paper and growth of plants.
Question 8.
State whether burning of a piece of paper is a reversible or an irreversible change.
Answer:
When we bum a piece of paper, it changes into ash and smoke. We cannot combine the ash and smoke to form the original piece of paper. So the burning of a piece of paper is an irreversible change.
Question 9.
Classify the following as reversible or irreversible changes:
(i) Growth of a plant
(ii) Ploughing a field,
(ii) Melting of wax
(iv) Falling of rain
(v) Pulling of rubber string
(vi) Breaking of a glass rod
(mi) Cooking of food.
Answer:
Reversible changes: (ii), (iii), (v)
Irreversible changes: (i), (iv), (vi), (vii).
Question 10.
How does curd set? Is this change reversible?
Answer:
A small quantity of curd is added to warm milk. The milk is stirred and is set aside undisturbed for a few hours at a warm place. In a few hours, the milk changes into curd.
Curd formed from milk cannot be changed into milk again. So, this is an irreversible change.
Question 11.
What are fast and slow changes?
Answer:
Fast changes take place over a short duration of time.
Slow changes take a longer duration of time to complete.
Question 12.
Define physical and chemical changes. Give examples.
Answer:
1. Physical change: Physical change is a temporary change in which chemical composition of the substance does not change and no new substance is formed.
During a physical change, only the physical properties of a substance change.
It is a reversible change. For example, melting of ice, during this change, the water changes from its solid form to liquid form. It can be solidified again.The water remains water in both the cases.
2. Chemical change: A chemical change is a permanent change in which not .
only the physical properties but chemical properties also change. It is an irreversible change. For example, formation of curd from milk, rusting of iron, etc.
Question 13.
Formation of clouds is a physical change. Explain.
Answer:
Formation of clouds is a physical change as it is phase transformation cycle of natural water from liquid to gas and then, gas to liquid. Hence, the property of water never changes in clouds form.
Question 14.
Explosion of a cracker is a chemical change. Explain.
Answer:
Explosion of crackers is a chemical change because the explosive reactants are transformed into gaseous products along with heat and light and thus cannot be reversed.
Hence, it is a chemical change.
Question 15.
Give some examples of physical and chemical changes.
Answer:
Examples of physical changes:
Tearing of sheet of paper into pieces, melting of ice, change of water into steam, breaking of glass tumbler, glowing of electric bulb, dissolution of sugar or salt in water.
Examples of chemical changes:
Burning of paper, wood, candle, etc., formation of curd from milk, cooking of food, rusting of iron and mixing of vinegar with baking soda, electrolysis of water.
Question 16.
Classify the following changes in as many ways as you can:
- Breaking of a brick with a hammer.
- Beating of heart.
- Germination of a seed.
- Burning of an incense-stick (agarbatti).
- Occurrence of solar eclipse.
Answer:
- Physical change, irreversible change.
- Periodic change, irreversible change.
- Irreversible change,
- Irreversible change, chemical change.
- Irreversible change.
Question 17.
Most physical changes are reversible. Give reasons with two examples.
Answer:
- Melting of ice: During this change, the water changes from its solid form to liquid form. It can be solidified again. The water remains water in both cases, hence reversible.
- Glowing of an electric bulb: During this change, electricity is passed through the tungston filament which becomes white hot and glows, but when the switch is off, the filament returns to its original shape and condition, hence totally reversible.
Question 18.
Give one example .each for physical and chemical changes
Answer:
Physical change (Melting of ice)
Question 19.
What is charring of sugar? Is it a chemical change?
Answer:
When sugar is continuously heated in the porcelain dish, it becomes foggy due to water vapour. A black powdery substance is left behind, which is charcoal. This process is also called charring of sugar and this is a chemical change.
Question 20.
Give some examples of changes which take place on their own.
Answer:
Question 21.
Give some examples of changes which take place on their own.
Answer:
Many changes are taking place around us on their own. For example:
- Ripening of crops in the fields.
- Leaves fall from trees.
- Flowers bloom and then wither away.
- Growing of hair and nail.
Could there be other ways to bring a change?
Question 1.
Does, like all other liquids, water expand on heating and contract on cooling?
Answer:
No, water is an exception. Water contracts on cooling till 4°C but expands when cooled further down from 4°C to 0°C.
Question 2.
List few ways to bring a change.
Answer:
- Heating or cooling
- Mixing two or more substances
- By applying force etc.
Question 3.
Give some examples from daily life where expansion of metal by heating is used. Explain.
Answer:
Fixing of a metal rim on an wooden wheel and fixing of wooden handles in iron blade in agricultural tools are such examples.
The iron blade of these tools has a ring in which the wooden handle is fixed. Normally, the ring is slightly smaller in size than the wooden handle. To fix the handle, the ring is heated and it becomes slightly larger in size (expands). Now, the handle easily fits into the ring. When the ring cools down, it contracts and fits tightly onto the handle.
Such a change is also used for fixing the metal rim on a wooden wheel of a«cart as shown in Fig. 6.4. Again the metal rim is made slightly smaller than the wooden wheel. On heating, the rim expands and fits onto the wheel. Cold water is then poured over the rim, which contracts and fits tightly onto the wheel.
Question 4.
Explain how a metal rim slightly smaller than a wooden wheel can be fixed on it.
Answer:
The metal rim is always made slightly smaller than the wooden wheel. The metal rim is heated; on heating, the rim expands and fits onto the wheel. Cold water is then poured over the rim. Due to cooling, rim contracts and fits tightly over the wheel.
Activity 7.
Take a small candle and measure its length with a scale. Now, fix it at a suitable place and light it. Let it burn for some time. Now blow out the candle and measure its length again (Fig.).
Its length will be reduced.
Can the change in the length of the candle be reversed? If we were to take some wax in a pan and heat it, can this change be reversed (Fig.)?
No, the change in the length of the candle cannot be reversed. Yes, on heating the wax in a pan, its change into liquid form can be reversed.
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