Question

The electrode potential of \( \mathrm{M^{2+}/M} \) of 3d-series elements shows positive value for :

• A. Fe
• B. Co
• C. Zn
• D. Cu

Hint:

Copper is the only 3d series metal that does not displace $H_2$ gas from dilute acids because its reduction potential is higher than that of $H^+$.

Answer 1

The Correct Option is D

Step 1: Most 3d transition metals have negative reduction potentials (they are more reactive than hydrogen).
Step 2: Copper has a positive $E^\circ = +0.34$ V.
Step 3: This is because the high energy to transform $Cu_{(s)}$ to $Cu^{2+}_{(aq)}$ is not compensated by its hydration enthalpy.