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Question (1)

QN0035824

Which observation alone can indicate that a chemical reaction may have taken place?

(A) Change in shape only
(B) Change in colour
(C) Change in size only
(D) Change in volume without any other change

Correct Answer: B

Explanation:

A change in colour is one of the observations that can indicate a chemical reaction. Other indicators include change in state, evolution of gas and change in temperature.

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Question (2)

QN0035825

In the reaction Mg + O₂ → MgO, which statement is correct?

(A) MgO is a reactant
(B) Mg and MgO are both products
(C) Mg and O₂ are reactants
(D) O₂ is a product

Correct Answer: C

Explanation:

Substances written on the left-hand side of the arrow are reactants, while the substance formed on the right-hand side is the product.

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Question (3)

QN0035826

Which of the following represents a balanced chemical equation?

(A) H₂ + O₂ → H₂O
(B) 2H₂ + O₂ → 2H₂O
(C) H₂ + 2O₂ → H₂O
(D) 2H₂ + 2O₂ → H₂O

Correct Answer: B

Explanation:

Both sides contain 4 hydrogen atoms and 2 oxygen atoms.

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Question (4)

QN0035827

Why is a chemical equation balanced?

(A) To increase the reaction rate
(B) To satisfy the law of conservation of mass
(C) To change the products
(D) To indicate the colour of reactants

Correct Answer: B

Explanation:

The number of atoms of every element must remain the same on both sides of a chemical equation.

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Question (5)

QN0035828

In a chemical equation, the symbol (aq) indicates that the substance is

(A) solid
(B) liquid
(C) present as a solution in water
(D) gaseous

Correct Answer: C

Explanation:

The symbol (aq) denotes an aqueous state, meaning the substance is present as a solution in water.

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Question (6)

QN0035829

What is the correct balanced equation for the formation of water from hydrogen and oxygen?

(A) H₂ + O₂ → H₂O
(B) 2H₂ + O₂ → 2H₂O
(C) H₂ + 2O₂ → 2H₂O
(D) 2H₂ + 2O₂ → H₂O

Correct Answer: B

Explanation:

The smallest whole-number coefficients that balance hydrogen and oxygen are 2, 1 and 2.

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Question (7)

QN0035830

A student writes Fe + H₂O → Fe₃O₄ + H₂. What is the coefficient of H₂O in the correctly balanced equation?

(A) 2
(B) 3
(C) 4
(D) 6

Correct Answer: C

Explanation:

The balanced equation is 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

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Question (8)

QN0035831

In the balanced equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂, the total number of hydrogen atoms on the reactant side is

(A) 4
(B) 6
(C) 8
(D) 10

Correct Answer: C

Explanation:

4H₂O contains 4 × 2 = 8 hydrogen atoms.

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Question (9)

QN0035832

If the equation 2Na + 2H₂O → 2NaOH + H₂ is considered, the ratio of Na atoms to H₂ molecules is

(A) 1 : 1
(B) 2 : 1
(C) 1 : 2
(D) 2 : 2

Correct Answer: B

Explanation:

The coefficients are 2 for Na and 1 for H₂, giving a ratio of 2:1.

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Question (10)

QN0035833

Which equation represents a combination reaction?

(A) CaCO₃ → CaO + CO₂
(B) Fe + CuSO₄ → FeSO₄ + Cu
(C) CaO + H₂O → Ca(OH)₂
(D) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

Correct Answer: C

Explanation:

Two reactants combine to form one product, so it is a combination reaction.

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Question (1)

Which observation alone can indicate that a chemical reaction may have taken place?

Explanation:

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Question (2)

In the reaction Mg + O₂ → MgO, which statement is correct?

Explanation:

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Question (3)

Which of the following represents a balanced chemical equation?

Explanation:

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Question (4)

Why is a chemical equation balanced?

Explanation:

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Question (5)

In a chemical equation, the symbol (aq) indicates that the substance is

Explanation:

Link:

Question (6)

What is the correct balanced equation for the formation of water from hydrogen and oxygen?

Explanation:

Link:

Question (7)

A student writes Fe + H₂O → Fe₃O₄ + H₂. What is the coefficient of H₂O in the correctly balanced equation?

Explanation:

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Question (8)

In the balanced equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂, the total number of hydrogen atoms on the reactant side is

Explanation:

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Question (9)

If the equation 2Na + 2H₂O → 2NaOH + H₂ is considered, the ratio of Na atoms to H₂ molecules is

Explanation:

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Question (10)

Which equation represents a combination reaction?

Explanation:

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