The metal from the first transition series having positive \(E_{M^{2+}/M}^0\) value:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cu
Copper is the only metal of the first transition series with a positive standard electrode potential, E°(\( \ce{Cu^{2+}} \)/Cu) = +0.34 V. Changing Cu(s) into Cu2+(aq) needs a large amount of energy (high enthalpy of atomisation plus the first and second ionisation enthalpies), and this is not balanced by its hydration enthalpy. So copper does not liberate \( \ce{H2} \) from acids. The other metals in the options have negative values: Cr −0.91 V, V −1.18 V and Ni −0.25 V.
NCERT (2026-27 edition):
Trends in the M2+/M Standard Electrode Potentials – …
