Question

The standard electrode potential $\left( M ^{3+} / M ^{2+}\right)$ 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

• A. $V ^{2+}$ and $Mn ^{2+}$
• B. $Mn ^{2+}$ and $Co ^{2+}$
• C. $Cr ^{2+}$ and $Co ^{2+}$
• D. $V ^{2+}$ and $Cr ^{2+}$

Answer 1

Answer: (D)

Metal cation with $(-)$ value of reduction potential $\left( M ^{+3} / M ^{+2}\right)$ or with $(+)$ value of oxidation potential $\left( M ^{+2} / M ^{+3}\right)$ will liberate $H _2$
Therefore they will reduce $H ^{+}$
i.eV ${ }^{+2}$ and $Cr ^{+2}$