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Question (31)

QN0035854

If 4 Cu atoms undergo complete oxidation according to 2Cu + O₂ → 2CuO, how many O₂ molecules are required?

(A) 1
(B) 2
(C) 3
(D) 4

Correct Answer: B

Explanation:

The ratio of Cu to O₂ is 2:1. Therefore, 4 Cu atoms require 2 O₂ molecules.

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Question (32)

QN0035855

In CuO + H₂ → Cu + H₂O, which substance is reduced?

(A) H₂
(B) CuO
(C) Cu
(D) H₂O

Correct Answer: B

Explanation:

CuO loses oxygen and changes into Cu, so CuO is reduced.

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Question (33)

QN0035856

In the same reaction, which substance is oxidised?

(A) CuO
(B) Cu
(C) H₂
(D) H₂O

Correct Answer: C

Explanation:

H₂ gains oxygen to form H₂O, so hydrogen is oxidised.

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Question (34)

QN0035857

A substance gains oxygen during a reaction. According to the chapter, this process is called

(A) reduction
(B) oxidation
(C) precipitation
(D) displacement

Correct Answer: B

Explanation:

Oxidation is defined as gain of oxygen or loss of hydrogen.

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Question (35)

QN0035858

A substance loses oxygen during a reaction. It is undergoing

(A) oxidation
(B) reduction
(C) combination
(D) precipitation

Correct Answer: B

Explanation:

Reduction is defined as loss of oxygen or gain of hydrogen.

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Question (36)

QN0035859

Consider ZnO + C → Zn + CO. Which pair correctly identifies the substances undergoing oxidation and reduction?

(A) ZnO oxidised; C reduced
(B) C oxidised; ZnO reduced
(C) Both oxidised
(D) Both reduced

Correct Answer: B

Explanation:

Carbon gains oxygen to form CO and is oxidised, while ZnO loses oxygen to form Zn and is reduced.

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Question (37)

QN0035860

In the reaction 4Na + O₂ → 2Na₂O, the number of sodium atoms on each side is

(A) 2
(B) 4
(C) 6
(D) 8

Correct Answer: B

Explanation:

The reactant side has 4 Na atoms. The product 2Na₂O also contains 2 × 2 = 4 Na atoms.

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Question (38)

QN0035861

In 4Na + O₂ → 2Na₂O, sodium is

(A) reduced because it loses oxygen
(B) oxidised because it gains oxygen
(C) reduced because it gains hydrogen
(D) unchanged

Correct Answer: B

Explanation:

Sodium combines with oxygen to form sodium oxide, so sodium gains oxygen and is oxidised.

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Question (39)

QN0035862

Which equation represents a redox reaction in which one reactant is oxidised while the other is reduced?

(A) CuO + H₂ → Cu + H₂O
(B) CaO + H₂O → Ca(OH)₂
(C) CaCO₃ → CaO + CO₂
(D) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Correct Answer: A

Explanation:

In CuO + H₂ → Cu + H₂O, CuO is reduced and H₂ is oxidised. Therefore, it is a redox reaction.

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Question (40)

QN0035863

A reaction absorbs energy supplied in the form of heat. Such a reaction is classified as

(A) exothermic
(B) endothermic
(C) precipitation
(D) displacement

Correct Answer: B

Explanation:

Endothermic reactions are reactions in which energy is absorbed.

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Question (31)

If 4 Cu atoms undergo complete oxidation according to 2Cu + O₂ → 2CuO, how many O₂ molecules are required?

Explanation:

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Question (32)

In CuO + H₂ → Cu + H₂O, which substance is reduced?

Explanation:

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Question (33)

In the same reaction, which substance is oxidised?

Explanation:

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Question (34)

A substance gains oxygen during a reaction. According to the chapter, this process is called

Explanation:

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Question (35)

A substance loses oxygen during a reaction. It is undergoing

Explanation:

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Question (36)

Consider ZnO + C → Zn + CO. Which pair correctly identifies the substances undergoing oxidation and reduction?

Explanation:

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Question (37)

In the reaction 4Na + O₂ → 2Na₂O, the number of sodium atoms on each side is

Explanation:

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Question (38)

In 4Na + O₂ → 2Na₂O, sodium is

Explanation:

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Question (39)

Which equation represents a redox reaction in which one reactant is oxidised while the other is reduced?

Explanation:

Link:

Question (40)

A reaction absorbs energy supplied in the form of heat. Such a reaction is classified as

Explanation:

Link:

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