JEE Main 2025 · 29 January · morning · Single correct · +4 / −1
The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity.
- (a) Eᵒ_(Sn⁴⁺/Sn²⁺) = +1.15 V
- (b) Eᵒ_(Al³⁺/Al) = -1.66 V
- (c) Eᵒ_(Pb⁴⁺/Pb²⁺) = +1.67 V
- (d) Eᵒ_(Tl³⁺/Tl) = +1.26 V
Answer and solution
Answer (c) Eᵒ_(Pb⁴⁺/Pb²⁺) = +1.67 V
Solution
Chemistry ma’am · 3 steps
The ion that most wants electrons wins: just pick the most positive reduction potential.
- What oxidising means. An oxidising agent takes electrons from something else, so it gets reduced itself. The stronger its pull for electrons, the stronger it is as an oxidant.
- Read the potential. E°_(red) measures how readily the oxidised form takes electrons. The more positive the value, the greater its tendency to get reduced.
Couple E°_(red) Oxidising species Sn⁴⁺/Sn²⁺ +1.15 V Sn⁴⁺ Al³⁺/Al -1.66 V Al³⁺, the weakest Pb⁴⁺/Pb²⁺ +1.67 V, highest Pb⁴⁺ Tl³⁺/Tl +1.26 V Tl³⁺ - So. Pb⁴⁺ has the most positive reduction potential, +1.67 V, so it is the strongest oxidising agent. This matches the inert pair effect: Pb²⁺ is far more stable than Pb⁴⁺, so Pb⁴⁺ readily gains two electrons. The answer is (c).
The idea to keep. More positive E°_(red) means a stronger oxidising agent. More negative E°_(red) means the reduced form is a stronger reducing agent.
Answer from the NTA final answer key. Solution by PrepWiser.