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Q-1: Which of the following is a change that can be reversed?
a) Batter to Idli
b) Grain to its flour
c) Milk to paneer
d) Stretched rubber band to its normal size
Answer: d) Stretched rubber band to its normal size
Explanation: The changes that can be reversed are those that, after taking place, can regain their original shape and size. Because the rubber band can return to its original shape after stretching, the change is reversible. While all other changes are irreversible.
Q-2: Which of the following changes that occur in our bodies is reversible?
a) Increase in height
b) Decrease in weight
c) Growing of nails
d) None of the above
Answer: d) None of the above
Explanation: All of the changes that occur in the body, such as height gain, weight loss, and nail growth, cannot be reversed naturally. As a result, they are not reversible changes.
Q-3: Melting of wax is a physical change because it involves
a) Change in the state from solid to liquid
b) Change in state from liquid to vapours
c) Change in state from solid to vapours
d) Change in state from liquid to solid
Answer: a) Change in the state from solid to liquid
Explanation: In the given process, only the physical state of a substance changes from solid to liquid, and no new products are formed. Therefore, the melting of wax is a physical change.
Q-4: A chemical change is also known as
a) Chemical process
b) Chemical reaction
c) Chemical activity
d) Chemical specie
Answer: b) Chemical reaction
Q-5: Cow dung to biogas is a chemical change. Why?
a) Because biogas can be converted back to cow dung.
b) Because a new product is formed.
c) Both a) and b)
d) Because chemical composition remains the same.
Answer: b) Because a new product is formed.
Explanation: Cow dung to biogas is a chemical transformation because the biogas produced (a new product) cannot be converted back to cow dung, and the compositions of biogas and cow dung are completely different. All of these are indications of a chemical change.
Q-6: The black material for repairing road is
a) Heated
b) Cooled
c) Both heated and cooled
d) None of the above
Answer: a) Heated
Q-7: What is the best way to effect change?
(a) Substance heating
(b) Substance cooling
(c) Combining one substance with another
(d) All of the above
Answer: d) All of the above
Q-8: Which of the following changes in water state is a physical change?
a) Melting
b) Condensation
c) Boiling
d) All of the above
Answer: d) All of the above
Explanation: Water’s state changes from solid to liquid during melting. Condensation converts vapours to liquid, whereas boiling converts liquids to vapours. Thus, water does not transform into a new substance. Only water undergoes state transitions. The form of water can be easily reversed. So, we can draw the conclusion that the water state is a physical change.
Q-9: How is clothing drying a reversible change?
a) Because the dried clothes cannot be re-wet
b) Because dry clothing can become wet again
c) Because all of the water from the clothes had evaporated
d) All of the above
Answer: b) Because dry clothing can become wet again
Explanation: Because the change can be reversed by wetting the dry clothes again, it is reversible.
Q-10: Which of the following is an irreversible change?
a) Shortening the length of the dress by folding
b) Cooking of food
c) Melting of ice
d) Cold milk to hot milk
Answer: b) Cooking of food
Explanation: An irreversible change is one that, once made, cannot be returned to its original shape, form, or size. Because food cannot be reversed back into the raw materials from which it is made, it is an irreversible change.
Q-11: Irreversible changes are _________ and ________.
a) Physical, temporary
b) Chemical, temporary
c) Physical, permanent
d) Chemical, permanent
Answer: d) Chemical, permanent
Explanation: Because irreversible changes result in the formation of new products, they are chemical changes, and because they cannot be reversed, they are also permanent changes.
Q-12: The metal rim is attached to the wooden cartwheel by
a) Heating the metal rim
b) Heating wooden wheel
c) Cooling metal rim
d) Cooling wooden wheel
Answer: a) Heating the metal rim
Explanation: Metal rings expand and fit around the wheel as they heat up.
Q-13: What happens when water is heated in a pan?
a) Quantity of the water in the pan increases
b) Water starts to cool up
c) Quantity of the water in the pan decreases
d) Water changes into solid
Answer: c) Quantity of the water in the pan decreases
Explanation: When we heat water in a pan, it eventually begins to boil. As we continue to heat, the amount of water in the pan begins to decrease. Water evaporates and becomes vapour.
Q-14: The shape and size of a pencil and eraser change with repeated use. Is it possible to undo this change?
a) Yes, to some extent
b) No
c) May be
d) Data insufficient
Answer: b) No
Explanation: It is impossible to undo the change once the shape and size of the pencil and eraser change after repeated use because it is an irreversible change, and irreversible changes are permanent and cannot be reversed.
Q-15: Which of the following is the name given to the process of converting a solid into a liquid?
a) Condensation
b) Melting
c) Evaporation
d) Freezing
Answer: b) Melting
Explanation: The process of converting a solid into a liquid is known as melting.
Q-16: Rusting or iron is an example of
a) Reversible change
b) Irreversible change
c) Physical change
d) None of the above
Answer: b) Irreversible Change
Explanation: Rusting of iron is an irreversible change because rust forms on the surface of iron articles during rusting. Once rusted, the iron article loses its strength and many other properties. And this change is permanent and irreversible.
Q-17: What kind of change is expansion?
a) Irreversible
b) Permanent
c) Reversible
d) All of the above
Answer: c) Reversible
Explanation: When an object is heated, its size expands. Expansion refers to the increase in size caused by heating. It is a reversible change because when a hot object cools, it shrinks and returns to its original size.
Q-18: Which of the following processes is responsible for recovering salt from water?
a) Condensation
b) Evaporation
c) Crystallisation
d) Melting
Answer: b) Evaporation
Explanation: When salt is dissolved in water, a salt solution is formed. Salt underwent a change during the formation of salt solution (as salt has disappeared into water). This change can be reversed by placing the salt solution beaker over a burner and allowing it to evaporate. Water is removed through evaporation while leaving the salt behind.
Q-19: Which of the following is not an example of a change that occurs when two substances are mixed?
a) Salt dissolved in water
b) Sand-water mixture
c) Sugar dissolved in water
d) Matchstick combustion
Answer: d) Matchstick combustion
Explanation: Matchick combustion is the burning of a matchstick. For burning to occur, no mixing is required.
Q-20: A chemical change involves
a) Both a change in state and a change in composition.
b) Only a state change
c) Only a colour change
d) None of the above
Answer: a) both a change in state and a change in composition.
Explanation: A chemical change is always accompanied by the formation of one or more new substances (s). A chemical change affects the physical and chemical properties of a substance, including its composition.
