Question:
Which of the following is NOT a redox reaction?
Which of the following is NOT a redox reaction?
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A redox reaction must show a change in oxidation number, and a neutralisation does not.
Updated On: Oct 1, 2026
- \(\text{Zn}+\text{H}_2\text{SO}_4\rightarrow \text{ZnSO}_4+\text{H}_2\)
- \(\text{Al(OH)}_3+3\text{HCl}\rightarrow \text{AlCl}_3+3\text{H}_2\text{O}\)
- \(\text{Mg}+1/2\text{O}_2\rightarrow \text{Mg}^{2+}+\text{O}^{2-}\)
- \(\text{Fe}_{(s)}+\text{Cu}_{(aq)}^{2+}\rightarrow \text{Fe}_{(aq)}^{2+}+\text{Cu}_{(s)}\)
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
A redox reaction involves a change in oxidation number of at least one element, which means electron transfer. If no element changes its oxidation number, it is not redox.
Step 2: Check option (A).
Zn goes from 0 to +2 and H goes from +1 to 0. Oxidation numbers change, so it is redox.
Step 3: Check option (B).
\(\text{Al(OH)}_3 + 3\text{HCl} \to \text{AlCl}_3 + 3\text{H}_2\text{O}\). Al stays +3, Cl stays -1, H stays +1 and O stays -2. Nothing changes. This is an acid-base neutralisation, so it is NOT redox.
Step 4: Check option (C).
Mg goes from 0 to +2 and O goes from 0 to -2. This is redox.
Step 5: Check option (D).
Fe goes from 0 to +2 and \(\text{Cu}^{2+}\) goes to Cu(0). This is redox, a displacement reaction.
Final Answer:
Only reaction (B) has no change in oxidation numbers. \[ \boxed{\text{(B)}} \]
A redox reaction involves a change in oxidation number of at least one element, which means electron transfer. If no element changes its oxidation number, it is not redox.
Step 2: Check option (A).
Zn goes from 0 to +2 and H goes from +1 to 0. Oxidation numbers change, so it is redox.
Step 3: Check option (B).
\(\text{Al(OH)}_3 + 3\text{HCl} \to \text{AlCl}_3 + 3\text{H}_2\text{O}\). Al stays +3, Cl stays -1, H stays +1 and O stays -2. Nothing changes. This is an acid-base neutralisation, so it is NOT redox.
Step 4: Check option (C).
Mg goes from 0 to +2 and O goes from 0 to -2. This is redox.
Step 5: Check option (D).
Fe goes from 0 to +2 and \(\text{Cu}^{2+}\) goes to Cu(0). This is redox, a displacement reaction.
Final Answer:
Only reaction (B) has no change in oxidation numbers. \[ \boxed{\text{(B)}} \]
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