JEE Main 2026 — Jan 23, Shift 1 — Chemistry solution

JEE Main2026Jan 23, Shift 1Chemistry

In the given electrochemical cell, Ag(s)|AgCl(s)|FeCl $_{2}$ (aq), FeCl $_{3}$ (aq)|Pt(s) at 298 K, the cell potential ( $E_{cell}$ ) will increase when :

(A) Concentration of Fe $^{2 +}$ is increased.

(B) Concentration of Fe $^{3 +}$ is decreased

(D) Concentration of Fe $^{3 +}$ is increased

(E) Concentration of Cl $^{-}$ is increased

Choose the correct answer from the options given below :

A
A and B only
B
A and E only
C
B only
D
C, D and E only

Solution

Cell reaction. Anode (Ag): Ag + Cl $^{-}$ → AgCl + e $^{-}$ . Cathode (Pt): Fe $^{3 +}$ + e $^{-}$ → Fe $^{2 +}$ . Net: Ag(s) + Cl $^{-}$ + Fe $^{3 +}$ → AgCl(s) + Fe $^{2 +}$ .

Nernst:

$E_{cell} = E_{cell}^{\circ} - \frac{0.059}{1} lo g \frac{[ Fe ^{2 +} ]}{[ Cl ^{-} ] [ Fe ^{3 +} ]}$

To make $E_{cell}$ larger, we need the log term to be more negative — that is, decrease the numerator or increase the denominator:

Options (A) and (B) do the opposite. $∴$ C, D and E only.

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