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Question (21)

QN001221

Which of the following changes is permanent because energy release forms new substances?

(A) Ice melting
(B) Wax softening
(C) Burning candle wick
(D) Folding paper

Correct Answer: C

Explanation:

Burning forms new substances and releases heat.

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Question (22)

QN001222

A student observes steam condensing back into water. This demonstrates that

(A) all changes are permanent
(B) some physical changes are reversible
(C) condensation forms new substances
(D) water is chemically changed

Correct Answer: B

Explanation:

Water vapour changes back into liquid water.

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Question (23)

QN001223

Which process is least likely to be reversed practically?

(A) Melting wax
(B) Folding cloth
(C) Burning coal
(D) Stretching spring

Correct Answer: C

Explanation:

Burning coal forms gases and ash permanently.

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Question (24)

QN001224

Which of the following best represents a reversible change involving temperature?

(A) Burning wood
(B) Melting and freezing water
(C) Cooking vegetables
(D) Rusting bicycle chain

Correct Answer: B

Explanation:

Water changes between liquid and solid states reversibly.

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Question (25)

QN001225

Which example shows that appearance may change while the substance remains the same?

(A) Burning paper
(B) Rusting iron
(C) Folding aluminium foil
(D) Digestion of food

Correct Answer: C

Explanation:

Folding changes shape but not composition.

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Question (26)

QN001226

Which of the following changes involves formation of ash?

(A) Melting wax
(B) Boiling water
(C) Burning wood
(D) Stretching rubber

Correct Answer: C

Explanation:

Burning wood forms ash.

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Question (27)

QN001227

Which process demonstrates a reversible change caused by cooling?

(A) Condensation of steam
(B) Burning magnesium ribbon
(C) Rusting iron
(D) Cooking food

Correct Answer: A

Explanation:

Steam changes back into water on cooling.

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Question (28)

QN001228

Which characteristic is most common in irreversible changes?

(A) No energy change
(B) No colour change
(C) New substances are formed
(D) Only shape changes

Correct Answer: C

Explanation:

Formation of new substances indicates irreversibility.

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Question (29)

QN001229

Which process below is an example of a reversible change in daily life?

(A) Inflating and deflating a balloon
(B) Burning firecrackers
(C) Baking biscuits
(D) Cooking rice

Correct Answer: A

Explanation:

A balloon can return to its original size after deflation.

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Question (30)

QN001230

Why is cooking food generally irreversible?

(A) Food becomes cold
(B) Food changes shape only
(C) New substances and flavours form
(D) Water evaporates only

Correct Answer: C

Explanation:

Cooking changes the chemical composition of food.

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Question (21)

Which of the following changes is permanent because energy release forms new substances?

Explanation:

Link:

Question (22)

A student observes steam condensing back into water. This demonstrates that

Explanation:

Link:

Question (23)

Which process is least likely to be reversed practically?

Explanation:

Link:

Question (24)

Which of the following best represents a reversible change involving temperature?

Explanation:

Link:

Question (25)

Which example shows that appearance may change while the substance remains the same?

Explanation:

Link:

Question (26)

Which of the following changes involves formation of ash?

Explanation:

Link:

Question (27)

Which process demonstrates a reversible change caused by cooling?

Explanation:

Link:

Question (28)

Which characteristic is most common in irreversible changes?

Explanation:

Link:

Question (29)

Which process below is an example of a reversible change in daily life?

Explanation:

Link:

Question (30)

Why is cooking food generally irreversible?

Explanation:

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