JEE Main · 2023 · Shift-IeasyRDX-004

Which of the following options are correct for the reaction? 2[{Au(CN)_2}]^{-}({aq}) + {Zn}({s}) 2{Au}({s}) +…

Redox Reactions · Class 11 · JEE Main Previous Year Question

Question

Which of the following options are correct for the reaction?

2[Au(CN)2]−(aq)+Zn(s)→2Au(s)+[Zn(CN)4]2−(aq)2[\mathrm{Au(CN)_2}]^{-}(\mathrm{aq}) + \mathrm{Zn}(\mathrm{s}) \rightarrow 2\mathrm{Au}(\mathrm{s}) + [\mathrm{Zn(CN)_4}]^{2-}(\mathrm{aq}) A. Redox reaction \quad B. Displacement reaction \quad C. Decomposition reaction \quad D. Combination reaction

Choose the correct answer from the options given below:

Options
  1. a

    A only

  2. b

    A and D only

  3. c

    A and B only

    ✓
  4. d

    C and D only

Correct Answerc

A and B only

Detailed Solution

Step 1 — Identify oxidation state changes:

  • Au\mathrm{Au} in [Au(CN)2]−[\mathrm{Au(CN)_2}]^-: Let x+2(−1)=−1⇒x=+1x + 2(-1) = -1 \Rightarrow x = +1
  • Au\mathrm{Au} in product: 00 → Reduced (gain of electrons)
  • Zn\mathrm{Zn} in reactant: 00
  • Zn\mathrm{Zn} in [Zn(CN)4]2−[\mathrm{Zn(CN)_4}]^{2-}: x+4(−1)=−2⇒x=+2x + 4(-1) = -2 \Rightarrow x = +2 → Oxidised

Since oxidation states change → A. Redox reaction ✓

Step 2 — Displacement reaction: Zn (more active metal) displaces Au from its complex salt → B. Displacement reaction ✓

Step 3 — Decomposition / Combination: No single compound breaks down (not decomposition ✗). No single product formed from multiple reactants (not combination ✗).

Answer: Option (3) — A and B only

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