Question

Which of the following is NOT a redox reaction?

• A. \(\text{Zn}+\text{H}_2\text{SO}_4\rightarrow \text{ZnSO}_4+\text{H}_2\)
• B. \(\text{Al(OH)}_3+3\text{HCl}\rightarrow \text{AlCl}_3+3\text{H}_2\text{O}\)
• C. \(\text{Mg}+1/2\text{O}_2\rightarrow \text{Mg}^{2+}+\text{O}^{2-}\)
• D. \(\text{Fe}_{(s)}+\text{Cu}_{(aq)}^{2+}\rightarrow \text{Fe}_{(aq)}^{2+}+\text{Cu}_{(s)}\)

Hint:

A redox reaction must show a change in oxidation number, and a neutralisation does not.

Answer 1

The Correct Option is B

Step 1: Method: track oxidation numbers.
Write the number of each element on both sides and look for any change.

Step 2: Go through the reactions.
(A) Zn: 0 to +2, H: +1 to 0. (C) Mg: 0 to +2, O: 0 to -2. (D) Fe: 0 to +2, Cu: +2 to 0. All three show electron transfer.

Step 3: The odd one.
In (B) every element keeps its oxidation number: Al +3, O -2, H +1, Cl -1. A base reacting with an acid to give salt and water has no electron transfer.

Final Answer:
Option (B) is not a redox reaction. \[ \boxed{\text{(B)}} \]