Which of the following options are correct for the reaction
2[Au(CN)₂]⁻(aq)+Zn(s) → 2 Au(s)+[Zn(CN)₄]²⁻(aq)
A. Redox reaction
B. Displacement reaction
C. Decomposition reaction
D. Combination reaction
Choose the correct answer from the options given below:

Solution

Chemistry ma’am · 5 steps

Track gold and zinc oxidation numbers, then see who pushes whom out of the complex.

1. Oxidation numbers. In [Au(CN)₂]⁻, each CN⁻ is -1, so Au is +1. It ends as Au(s) at 0. Zinc starts at 0 and becomes +2 in [Zn(CN)₄]²⁻.
2. Redox. Gold is reduced (+1 → 0) and zinc is oxidised (0 → +2). Both changes happen together, so this is a redox reaction.
3. Displacement. Zinc is more reactive than gold, so it takes gold's place and binds the CN⁻ ions, and gold comes out as the free metal. One metal pushing another out is a displacement reaction. This is how gold is recovered in the cyanide process.
4. Not C or D. Two reactants give two products. Nothing breaks into simpler parts, so it is not decomposition. Nothing joins into a single product, so it is not combination.
5. So. Statements A and B are correct, which is option (a).

The idea to keep. A metal pushing a less reactive metal out of its compound is always both displacement and redox. The displacing metal is oxidised and the displaced one is reduced.

Answer from the NTA final answer key. Solution by PrepWiser.