Standard reduction potentials (E°) of \(Pb^{2+}, Ag^+, Cu^{2+}\) and \(Fe^{2+}\) are -0.13 V, +0.80 V, +0.31 V, -0.44 V respectively. Which of the following metals is the strongest reducing agent?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Fe
A reducing agent is itself oxidised, so among metals the strongest reducing agent is the one that loses electrons most easily: the one with the most negative standard reduction potential of its Mn+/M couple.
\( \displaystyle E^\circ:\ \ce{Fe^2+/Fe} = -0.44\ \mathrm{V} \lt \ce{Pb^2+/Pb} = -0.13\ \mathrm{V} \lt \ce{Cu^2+/Cu} = +0.31\ \mathrm{V} \lt \ce{Ag+/Ag} = +0.80\ \mathrm{V} \)
Reducing strength therefore falls in the order Fe > Pb > Cu > Ag, and iron, with the lowest E°, is the strongest reducing agent.
Why the other options are incorrect
Option (2) Cu — Incorrect. E° = +0.31 V is positive, so copper is a weaker reducing agent than hydrogen and much weaker than iron.
Option (3) Pb — Incorrect. E° = −0.13 V is less negative than that of iron, so lead is the weaker reducing agent.
Option (4) Ag — Incorrect. E° = +0.80 V is the highest of the four, so silver is the weakest reducing agent (\( \ce{Ag^{+}} \) is the strongest oxidising agent).
NCERT (2026-27 edition):
Measurement of Electrode Potential – “… 1. A negative Eo means that the redox couple is a stronger reducing agent than the H+/H2 couple. 2. A positive Eo means that the redox couple is a weaker reducing agent than the H+/H2 couple.”