JEE Main 2026 — Jan 23, Shift 2 — Chemistry solution

JEE Main2026Jan 23, Shift 2Chemistry

Consider the above electrochemical cell where a metal electrode (M) is undergoing redox reaction by forming $M^{+}$ ( $M \to M^{+} + e$ ). The cation $M^{+}$ is present in two different concentrations $c_{1}$ and $c_{2}$ as shown above. Which of the following statement is correct for generating a positive cell potential?

A
If $c_{1}$ is present at anode, then $c_{1} = c_{2}$
B
If $c_{1}$ is present at cathode, then $c_{1} < c_{2}$
C
If $c_{1}$ is present at cathode, then $c_{1} > c_{2}$
D
If $c_{1}$ is present at anode, then $c_{1} > c_{2}$

Solution

This is a concentration cell. The Nernst equation gives:

$E_{ce l l} = - \frac{0.059}{1} lo g \frac{[ M ^{+} ] _{an o d e}}{[ M ^{+} ] _{c a t h o d e}}$

Case 1: $c_{1}$ at cathode, $c_{2}$ at anode.

$E_{ce l l} = - 0.059 lo g \frac{c _{2}}{c _{1}}$

For $E_{ce l l} > 0$ , we need $\frac{c _{2}}{c _{1}} < 1$ , i.e. $c_{1} > c_{2}$ .

Case 2: $c_{1}$ at anode, $c_{2}$ at cathode.

$E_{ce l l} = - 0.059 lo g \frac{c _{1}}{c _{2}} > 0 \Rightarrow c_{2} > c_{1}$ .

Only option (3) matches a valid positive-potential scenario.

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