Standard electrode potentials for a few half cells are mentioned below: E Cu 2+ / Cu 0 =0.34 V , E Zn 2+ / Zn 0 =-0.76 V E Ag + / Ag 0 =0.80 V , E Mg 2+ / Mg 0 =-2.37 V Which one of the following cells gives the most negative value of Δ G o ?

Zn Zn 2+ (1 M ) \ Ag + (1 M ) Ag

Zn Zn 2+ (1 M ) Mg 2+ (1 M ) Mg

Cu Cu 2+ (1 M ) \ Ag + (1 M ) Ag

Chemistry · Electrochemistry

JEE Main 2025 — 23 January, Evening Shift — Question 27

Standard electrode potentials for a few half cells are mentioned below:

$\mathrm{E}_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{0}=0.34 \mathrm{~V}, \mathrm{E}_{\mathrm{Zn}^{2+} / \mathrm{Zn}}^{0}=-0.76 \mathrm{~V}$

$\mathrm{E}_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{0}=0.80 \mathrm{~V}, \mathrm{E}_{\mathrm{Mg}^{2+} / \mathrm{Mg}}^{0}=-2.37 \mathrm{~V}$

Which one of the following cells gives the most negative value of $\Delta \mathrm{G}^{\mathrm{o}}$ ?

Option A:
$\mathrm{Zn}\left|\mathrm{Zn}^{2+}(1 \mathrm{M}) \| \mathrm{Ag}^{+}(1 \mathrm{M})\right| \mathrm{Ag}$
Correct
Option B:
$\mathrm{Zn}\left|\mathrm{Zn}^{2+}(1 \mathrm{M})\right|\left|\mathrm{Mg}^{2+}(1 \mathrm{M})\right| \mathrm{Mg}$
Option C:
$\mathrm{Ag}\left|\mathrm{Ag}^{+}(1 \mathrm{M})\right|\left|\mathrm{Mg}^{2+}(1 \mathrm{M})\right| \mathrm{Mg}$
Option D:
$\mathrm{Cu}\left|\mathrm{Cu}^{2+}(1 \mathrm{M}) \| \mathrm{Ag}^{+}(1 \mathrm{M})\right| \mathrm{Ag}$

$\because \Delta \mathrm{G}^{\circ}=-\mathrm{nFE}^{\circ}$

Option (1) $\mathrm{E}^{\circ}=0.8+0.76$

$=1.56 \mathrm{~V}$

$\therefore \Delta \mathrm{G}^{\circ}=-2 \times \mathrm{F} \times 1.56$

$=-3.12 \mathrm{~V}$

Option (2) $\mathrm{E}^{\circ}=-2.37+0.76$

$=-1.61 \mathrm{~V}$

$\therefore \Delta \mathrm{G}^{\circ}=-2 \times \mathrm{F} \times(-1.61)$

$=+3.22 \mathrm{~V}$

Option (3) $\mathrm{E}^{\circ}=-2.37-0.8$

$=-3.17 \mathrm{~V}$

$\therefore \Delta \mathrm{G}^{\circ}=-2 \times \mathrm{F} \times(-3.17)$

=+6.34

Option (4) $\mathrm{E}^{\circ}=0.8-0.34$

=0.46 \mathrm{~V}

$\Delta \mathrm{G}^{\circ}=-2 \times \mathrm{F} \times 0.46$

=-0.92 \mathrm{~V}

Answer key and solution verified before publishing.

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