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

Options

A. A only
B. A and D only
C. A and B only
D. C and D only

Answer

To determine which options are correct for the given reaction:

\[ 2[Au(CN)_2]^{-} (aq) + Zn(s) \rightarrow 2Au(s) + [Zn(CN)_4]^{2-} (aq) \]

we will analyze the reaction step by step.

### Step 1: Identify the oxidation states of the elements involved.
- For \( [Au(CN)_2]^{-} \):
- Let the oxidation state of Au be \( x \).
- The cyanide ion \( CN^{-} \) has a charge of -1, and since there are 2 cyanide ions, the total contribution from them is -2.
- The overall charge of the complex is -1, so:
\[ x - 2 = -1 \implies x = +1 \]
Thus, the oxidation state of Au in \( [Au(CN)_2]^{-} \) is +1.

- For Zn(s):
- The oxidation state of Zn in its elemental form is 0.

- For Au(s):
- The oxidation state of Au in its elemental form is 0.

- For \( [Zn(CN)_4]^{2-} \):
- Let the oxidation state of Zn be \( y \).
- The contribution from 4 cyanide ions is -4 (since each \( CN^{-} \) has a charge of -1).
- The overall charge of the complex is -2, so:
\[ y - 4 = -2 \implies y = +2 \]
Thus, the oxidation state of Zn in \( [Zn(CN)_4]^{2-} \) is +2.

### Step 2: Determine the changes in oxidation states.
- Au changes from +1 in \( [Au(CN)_2]^{-} \) to 0 in Au(s) (reduction).
- Zn changes from 0 in Zn(s) to +2 in \( [Zn(CN)_4]^{2-} \) (oxidation).

### Step 3: Classify the reaction.
- Since there is a transfer of electrons (Au is reduced and Zn is oxidized), this is a **redox reaction**.
- Zn displaces Au from the complex because it is more reactive, indicating that this is also a **displacement reaction**.
- There is no decomposition of a single substance into simpler substances, nor is there a combination of two or more reactants to form one product.

### Conclusion:
The correct options for the reaction are:
- A. Redox reaction
- B. Displacement reaction

Thus, the answer is **A and B**.