Write the Nernst equation and calculate e.m.f. of the following cell at 298 K :
`Sn (s) |Sn^(2+) (0.050 M) ||H^(+) (0.20 M) |H_(2) ` (1 atm) |Pt.

Explanation

To solve the problem, we need to follow these steps:

### Step 1: Identify the half-reactions
In the given cell representation, we have:
- Anode (oxidation): \( \text{Sn (s)} \rightarrow \text{Sn}^{2+} + 2e^- \)
- Cathode (reduction): \( 2\text{H}^+ + 2e^- \rightarrow \text{H}_2 (g) \)

### Step 2: Write the overall cell reaction
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