The standard electrode potential ( $\mathrm{M}^{3+} / \mathrm{M}^{2+}$ ) for V , $\mathrm{Cr}$, $\mathrm{Mn}$ & $\mathrm{Co}$ are $-0.26 \mathrm{~V}$, $-0.41 \mathrm{~V}$, $+1.57 \mathrm{~V}$ and $+1.97 \mathrm{~V}$ , respectively. The metal ions which can liberate $\mathrm{H}_{2}$ from a dilute acid are

(C) $\mathrm{V}^{2+}$ and $\mathrm{Cr}^{2+}$

(A) $\mathrm{V}^{2+}$ and $\mathrm{Mn}^{2+}$

(B) $\mathrm{Cr}^{2+}$ and $\mathrm{Co}^{2+}$

(D) $\mathrm{Mn}^{2+}$ and $\mathrm{Co}^{2+}$

JEE Main · 2023 · 29 Jan 2023 · Shift 1 · Redox Reactions and Electrochemistry

The standard electrode potential (

M^{3 +} / M^{2 +}

) for V ,

Cr

Mn

Co

are

- 0.26 V

- 0.41 V

+ 1.57 V

and

+ 1.97 V

, respectively. The metal ions which can liberate

H_{2}

from a dilute acid are

Answer: (C)

A dipositive ion can set hydrogen free from a dilute acid only if

H^{+}

can oxidise it to the tripositive state, which is possible when the

M^{3 +} / M^{2 +}

reduction potential is negative. Among the given figures only vanadium (

- 0.26 V

) and chromium (

- 0.41 V

) are negative, while manganese (

+ 1.57 V

) and cobalt (

+ 1.97 V

) are strongly positive and their dipositive ions are stable towards acid. The ions that liberate hydrogen from dilute acid are therefore

V^{2 +}

and

C r^{2 +}

JEE Main · 2023 · 29 Jan 2023 · Shift 1 · Single correct option