Given below are few reactions with some expressions. Mark the expressions which is not correctly matched.

Options

A. For concentration cell, `Ag|Ag^(+)(C_1)||Ag^(+)(C_2)|Ag, E_"cell"=-0.0591/1"log"C_1/C_2`
B. For the cell , `2Ag^(+) +H_2 "(1 atm)" to 2Ag + 2H^(+) (1M) , E_"cell"=E_"cell"^@-0.0591/2"log"([Ag^+]^2)/[H^+]^2`
C. For an electrochemical reaction, at equilibrium `aA + bB overset("ne"^-) hArr cC + dD, E_"cell"^@=0.0591/n "log"([C]^c [D]^d)/([A]^a [B]^b)`
D. For the cell , `M_((aq))^(n+) + "ne"^(-) to M_((s)) , E=E^@-0.0591/n "log"1/([M^(n+)])`

Explanation

To solve the question regarding the incorrect matching of expressions with the given reactions, we will analyze each reaction and its corresponding expression step by step.

### Step 1: Understanding the Nernst Equation
The Nernst equation is given by:
\[ E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.0591}{n} \log \left( \frac{[\text{Products}]}{[\text{Reactants}]} \right) \]
where:
- \( E_{\text{cell}} \) = EMF of the cell
- \( E^\circ_{\text{cell}} \) = Standard EMF of the cell
- \( n \) = Number of electrons exchanged
- Concentrations of products and reactants are used in the logarithmic term.

### Step 2: Analyzing Each Reaction

**Reaction 1:**
- Given: \( \text{Ag} + \text{Ag}^+_{C1} \rightleftharpoons \text{Ag} + \text{Ag}^+_{C2} \)
- Anodic Reaction: \( \text{Ag} \rightarrow \text{Ag}^+ + e^- \)
- Cathodic Reaction: \( \text{Ag}^+ + e^- \rightarrow \text{Ag} \)
- Expression: \( E_{\text{cell}} = -\frac{0.0591}{1} \log \left( \frac{C1}{C2} \right) \)
- This expression is correct.

**Reaction 2:**
- Given: \( 2\text{Ag}^+ + \text{H}_2 \rightleftharpoons 2\text{Ag} + 2\text{H}^+ \)
- Anodic Reaction: \( \text{H}_2 \rightarrow 2\text{H}^+ + 2e^- \)
- Cathodic Reaction: \( 2\text{Ag}^+ + 2e^- \rightarrow 2\text{Ag} \)
- Expression: \( E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.0591}{2} \log \left( \frac{[\text{H}^+]^2}{[\text{Ag}^+]^2} \right) \)
- This expression is correct.

**Reaction 3:**
- Given: \( A + B \rightleftharpoons C + D \)
- At equilibrium, \( E_{\text{cell}} = 0 \)
- Expression: \( E_{\text{cell}} = \frac{0.0591}{n} \log \left( \frac{[C]^c[D]^d}{[A]^a[B]^b} \right) \)
- This expression is correct.

**Reaction 4:**
- Given: \( \text{M}^{n+} + n e^- \rightarrow \text{M (solid)} \)
- Expression: \( E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.0591}{n} \log \left( \frac{1}{[\text{M}^{n+}]} \right) \)
- This expression is correct.

### Step 3: Identifying the Incorrect Expression
After analyzing all the reactions and their corresponding expressions:
- The expression for **Reaction 2** is incorrectly matched because it states that \( \text{Ag}^+ \) is on the product side, while it is actually on the reactant side.

### Conclusion
The expression that is not correctly matched is for **Reaction 2**.