Which gas is produced when zinc reacts with dilute hydrochloric acid? MCQ with Answer and Explanation

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Which gas is produced when zinc reacts with dilute hydrochloric acid?

A. Carbon dioxide

B. Oxygen

C. Chlorine

D. Hydrogen

Answer: Option D

Solution (By JKExamLibrary)

Zn + 2HCl → ZnCl₂ + H₂↑. Zinc displaces hydrogen from acid because it is more reactive than hydrogen in the reactivity series. Hydrogen gas burns with a pop sound when a burning splint is brought near the mouth of the test tube. Metals above hydrogen in the series react with acids to evolve H₂; metals below (Cu, Ag) do not. Nitric acid is an oxidizer, so may not yield H₂.

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Question #1

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Assertion (A): A catalyst does not change the equilibrium yield of a reaction. Reason (R): A catalyst speeds up both the forward and backward reactions equally.

A. Both A and R are true but R is NOT the correct explanation of A.

B. A is false but R is true.

C. A is true but R is false.

D. Both A and R are true and R is the correct explanation of A.

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Correct Answer: Option D

Explanation:
A catalyst lowers the activation energy for both the forward and reverse reactions by the same amount. Therefore, it increases the rates of both reactions equally, allowing the system to reach equilibrium faster, but without changing the final equilibrium concentrations (yield). Both statements are correct and R explains A.

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Question #2

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Ionization energy generally decreases down a group because:

A. Electron affinity increases

B. Nuclear charge decreases

C. Atomic radius increases and shielding effect increases

D. Number of valence electrons increases

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Correct Answer: Option C

Explanation:
Down a group, number of shells increases, atomic radius increases, and inner electrons shield the outermost electron from the nucleus. The effective nuclear charge experienced by valence electron decreases, making it easier to remove. Thus ionization energy decreases. For example, IE of Cs

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Question #3

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The diagonal relationship in the periodic table is most prominently seen between:

A. Lithium and Magnesium

B. Boron and Silicon

C. Beryllium and Aluminum

D. All of the above

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Correct Answer: Option D

Explanation:
The diagonal relationship occurs when elements in the second period resemble elements in the third period of the next group due to similar ionic sizes and charge-to-radius ratios (polarizing power). Li-Mg, Be-Al, and B-Si are all classic examples of this phenomenon.

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