Question

$\mathrm{E}{°}_{{\mathrm{M}}^{2+}/\mathrm{M}}$ has a positive value for which of the following elements of 3d transition series?

• A. $\mathrm{Cu}$
• B. $\mathrm{Zn}$
• C. $\mathrm{Cr}$
• D. $\mathrm{Co}$

Answer 1

The correct option is A

$\mathrm{Cu}$

Explanation for correct option

A) $\mathrm{Cu}$

According to the electrochemical series, the elements present above $\mathrm{H}$ have positive $\mathrm{E}°$value. For ${{\mathrm{M}}^{2+}}_{\left(\mathrm{aq}\right)}/{\mathrm{M}}_{\left(\mathrm{s}\right)}$ out of the given options,${{\mathrm{Cu}}^{2+}}_{\left(\mathrm{aq}\right)}/{\mathrm{Cu}}_{\left(\mathrm{s}\right)}$ will be the correct answer.

${{\mathrm{Cu}}^{2+}}_{\left(\mathrm{aq}\right)}+2{\mathrm{e}}^{–}\to {\mathrm{Cu}}_{\left(\mathrm{s}\right)};\mathrm{E}°=+0.34\mathrm{V}$

Explanation for Incorrect options :

According to the electrochemical series, the other elements present above have negative $\mathrm{E}°$ values.

$$\begin{gathered} {{\mathrm{Zn}}^{2+}}_{\left(\mathrm{aq}\right)}+2{\mathrm{e}}^{–}\to {\mathrm{Zn}}_{\left(\mathrm{s}\right)};\mathrm{E}°=-0.763\mathrm{V} \\ {{\mathrm{Co}}^{2+}}_{\left(\mathrm{aq}\right)}+2{\mathrm{e}}^{-}\to {\mathrm{Co}}_{\left(\mathrm{s}\right)};\mathrm{E}°=-0.28\mathrm{V} \\ {{\mathrm{Cr}}^{2+}}_{\left(\mathrm{aq}\right)}+2{\mathrm{e}}^{–}\to {\mathrm{Cr}}_{\left(\mathrm{s}\right)};\mathrm{E}°=-0.9\mathrm{V} \end{gathered}$$