JEE Main · 2025 · 29 Jan 2025 · Shift 1 · Redox Reactions and Electrochemistry

The oxidising strength of a redox couple tracks its standard reduction potential directly — a higher (more positive) $E^{\ominus }$ means the oxidised form has a stronger pull for electrons and is therefore a stronger oxidiser. Comparing the four couples: $E_{{\mathrm{Sn}}^{4+}/{\mathrm{Sn}}^{2+}}^{\ominus }=+1.15\text{ V}$, $E_{{\mathrm{Tl}}^{3+}/\mathrm{Tl}}^{\ominus }=+1.26\text{ V}$, $E_{{\mathrm{Al}}^{3+}/\mathrm{Al}}^{\ominus }=-1.66\text{ V}$ (Al${}^{3+}$ is very hard to reduce, so it is a weak oxidiser), and $E_{{\mathrm{Pb}}^{4+}/{\mathrm{Pb}}^{2+}}^{\ominus }=+1.67\text{ V}$. The Pb${}^{4+}$/Pb${}^{2+}$ couple carries the largest positive potential of the set, making Pb${}^{4+}$ the strongest oxidising species.