The equilibrium `Cu^(0)+Cu^(||)hArr2Cu^(|)`
In the aqueous medium at `25^(@)C` shifts towards the left in the presence of
(1) `Cl^(-)` (2) `CN^(-)`(3) `SCN^(-)` (4) `NO_(3)^(-)`

Options

A. 1, 2
B. 2, 3
C. 1, 2, 3
D. 2, 3, 4

Answer

To solve the given equilibrium problem, we need to analyze the reaction and the effects of each ion on the equilibrium position. The equilibrium reaction is:

\[ \text{Cu}^{(0)} + \text{Cu}^{(II)} \rightleftharpoons 2 \text{Cu}^{(I)} \]

Where:
- \(\text{Cu}^{(0)}\) is elemental copper.
- \(\text{Cu}^{(II)}\) is copper in the +2 oxidation state.
- \(\text{Cu}^{(I)}\) is copper in the +1 oxidation state.

### Step-by-Step Solution:

1. **Identify the Equilibrium Shift**:
The equilibrium shifts to the left when the concentration of the products (\(\text{Cu}^{(I)}\)) decreases or the concentration of the reactants (\(\text{Cu}^{(0)}\) and \(\text{Cu}^{(II)}\)) increases.

2. **Analyze the Effect of Each Ion**:
- **Cl⁻ (Chloride Ion)**: Chloride ions do not form a stable complex with \(\text{Cu}^{(II)}\) and thus will not significantly affect the equilibrium. Therefore, it does not shift the equilibrium to the left.
- **CN⁻ (Cyanide Ion)**: Cyanide ions can react with \(\text{Cu}^{(II)}\) to form a stable complex \(\text{Cu(CN)}_4^{3-}\). This reduces the concentration of \(\text{Cu}^{(II)}\) in solution, which will shift the equilibrium to the left.
- **SCN⁻ (Thiocyanate Ion)**: Similar to cyanide, thiocyanate ions can also form a complex with \(\text{Cu}^{(II)}\) (e.g., \(\text{Cu(SCN)}_4^{3-}\)). This also reduces the concentration of \(\text{Cu}^{(II)}\) and shifts the equilibrium to the left.
- **NO₃⁻ (Nitrate Ion)**: Nitrate ions do not form complexes with copper ions and will not affect the equilibrium position significantly. Thus, it does not shift the equilibrium to the left.

3. **Conclusion**:
The equilibrium will shift to the left in the presence of CN⁻ and SCN⁻ ions. Therefore, the correct options are (2) CN⁻ and (3) SCN⁻.

### Final Answer:
The equilibrium shifts towards the left in the presence of:
- (2) CN⁻
- (3) SCN⁻