Q90 / 270 · NDA 2026 (Phase 1) · General Ability
Consider the following pairs of reactions and properties:
Reactions Properties I. $\text{Fe(s)} + 2\text{HCl(aq)} \rightarrow \text{FeCl}_2\text{(aq)} + \text{H}_2\text{(g)}$ Fe is reductant II. $\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)}$ Cu is being reduced III. $\text{Br}_2\text{(l)} + 2\text{I}^-\text{(aq)} \rightarrow 2\text{Br}^-\text{(aq)} + \text{I}_2\text{(s)}$ $\text{Br}_2$ is reductant IV. $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)}$ C atom in $\text{CH}_4$ is oxidized
Which of the above pairs are correct?
| Reactions | Properties |
|---|---|
| I. $\text{Fe(s)} + 2\text{HCl(aq)} \rightarrow \text{FeCl}_2\text{(aq)} + \text{H}_2\text{(g)}$ | Fe is reductant |
| II. $\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)}$ | Cu is being reduced |
| III. $\text{Br}_2\text{(l)} + 2\text{I}^-\text{(aq)} \rightarrow 2\text{Br}^-\text{(aq)} + \text{I}_2\text{(s)}$ | $\text{Br}_2$ is reductant |
| IV. $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)}$ | C atom in $\text{CH}_4$ is oxidized |
Which of the above pairs are correct?
- AI and II only
- BII, III and IV
- Correct answerCI, II and IV
- DI, III and IV
Solution
Reaction I: $\text{Fe}$ changes its oxidation state from $0$ to $+2$. It undergoes oxidation and acts as a reductant. Pair I is correct.
Reaction II: $\text{Cu}$ in $\text{CuSO}_4$ changes its oxidation state from $+2$ to $0$. It undergoes reduction. Pair II is correct.
Reaction III: $\text{Br}_2$ changes its oxidation state from $0$ to $-1$. It undergoes reduction and acts as an oxidant, not a reductant. Pair III is incorrect.
Reaction IV: $\text{C}$ in $\text{CH}_4$ changes its oxidation state from $-4$ to $+4$. It undergoes oxidation. Pair IV is correct.
Therefore, pairs I, II, and IV are correct.
Reaction II: $\text{Cu}$ in $\text{CuSO}_4$ changes its oxidation state from $+2$ to $0$. It undergoes reduction. Pair II is correct.
Reaction III: $\text{Br}_2$ changes its oxidation state from $0$ to $-1$. It undergoes reduction and acts as an oxidant, not a reductant. Pair III is incorrect.
Reaction IV: $\text{C}$ in $\text{CH}_4$ changes its oxidation state from $-4$ to $+4$. It undergoes oxidation. Pair IV is correct.
Therefore, pairs I, II, and IV are correct.
Hence, the correct answer is option: 'C'.