E.M.F. of `Ni(s) (ni^(2+) (aq)||Cu^(2+) (aq)| Cu(s)` cell can be increased by

Options

A. Adding `NH_(3)` in the right half -cell
B. Increasing the conc. Of `Ni^(2+)` ions
C. Adding dimethyl glyoxime into the left half-cell
D. Changing the electrolyte present in salt bridge

Answer

To solve the problem of how to increase the E.M.F. (Electromotive Force) of the cell represented by the reaction `Ni(s) | Ni^(2+) (aq) || Cu^(2+) (aq) | Cu(s)`, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Cell Components**:
- The cell consists of two half-cells:
- Anode: Nickel (Ni) oxidizing to Ni²⁺.
- Cathode: Copper (Cu²⁺) reducing to Cu.

2. **Write the Half-Reactions**:
- Anode reaction:
\[ Ni(s) \rightarrow Ni^{2+}(aq) + 2e^- \]
- Cathode reaction:
\[ Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \]

3. **Overall Cell Reaction**:
- The overall cell reaction can be written as:
\[ Cu^{2+}(aq) + Ni(s) \rightarrow Ni^{2+}(aq) + Cu(s) \]

4. **Nernst Equation**:
- The E.M.F. of the cell can be calculated using the Nernst equation:
\[ E_{cell} = E^\circ_{cell} - \frac{RT}{nF} \ln Q \]
- Where \( Q \) is the reaction quotient given by:
\[ Q = \frac{[Ni^{2+}]}{[Cu^{2+}]} \]

5. **Understanding the Effect of Concentrations**:
- To increase the E.M.F., we need to manipulate the reaction quotient \( Q \). A lower value of \( Q \) will lead to a higher E.M.F.
- This can be achieved by decreasing the concentration of Ni²⁺ or increasing the concentration of Cu²⁺.

6. **Options Analysis**:
- **Adding NH₃**: This does not affect the concentrations of Ni²⁺ or Cu²⁺ directly.
- **Increasing Ni²⁺ concentration**: This will increase \( Q \), which is not desired.
- **Adding dimethylglyoxime (DMG)**: DMG forms a complex with Ni²⁺, effectively reducing its concentration in the solution, thus decreasing \( Q \) and increasing E.M.F.
- **Changing the electrolyte**: This does not affect the concentrations of the ions involved in the half-reactions.

7. **Conclusion**:
- The best way to increase the E.M.F. of the cell is by adding dimethylglyoxime to the left half-cell, which will bind to Ni²⁺ and reduce its concentration.

### Final Answer:
The E.M.F. of the cell can be increased by **adding dimethylglyoxime into the left half-cell**.