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 problem, we need to analyze the equilibrium reaction given:

\[ \text{Cu}^{0} + \text{Cu}^{2+} \rightleftharpoons 2\text{Cu}^{+} \]

We want to determine which of the given ions will shift the equilibrium to the left (towards the reactants) when added to the system.

### Step 1: Understand the Equilibrium
The equilibrium involves solid copper (Cu^0) and copper ions in two different oxidation states (Cu^2+ and Cu^+). According to Le Chatelier's principle, if we decrease the concentration of the products or increase the concentration of the reactants, the equilibrium will shift to the left.

### Step 2: Analyze Each Ion
1. **Cl⁻ (Chloride Ion)**:
- When Cl⁻ is added, it reacts with Cu²⁺ to form a precipitate (CuCl₂). This decreases the concentration of Cu²⁺ in the solution.
- Since Cu²⁺ is a reactant, its decrease will shift the equilibrium to the left.

2. **CN⁻ (Cyanide Ion)**:
- CN⁻ can also react with Cu²⁺ to form a precipitate (CuCN). This again decreases the concentration of Cu²⁺.
- Thus, the equilibrium will also shift to the left.

3. **SCN⁻ (Thiocyanate Ion)**:
- SCN⁻ reacts with Cu²⁺ to form a precipitate (Cu(SCN)₂). This decreases the concentration of Cu²⁺.
- Therefore, the equilibrium will shift to the left as well.

4. **NO₃⁻ (Nitrate Ion)**:
- NO₃⁻ does not form any precipitate with Cu²⁺ and does not affect its concentration.
- Hence, the equilibrium will not shift in either direction when NO₃⁻ is added.

### Conclusion
The ions that shift the equilibrium to the left are Cl⁻, CN⁻, and SCN⁻. The only ion that does not affect the equilibrium is NO₃⁻.

### Final Answer
The correct options that shift the equilibrium to the left are:
- (1) Cl⁻
- (2) CN⁻
- (3) SCN⁻