JEE Main 2024 — 5 April, Shift 2 — Question 76

An ion can liberate hydrogen from a dilute acid if it acts as a strong reducing agent, i.e., if it can be easily oxidised and has a standard reduction potential more negative than that of the $\mathrm{H^+/H_2}$ electrode.

$\mathrm{Ti}^{2+}$: Titanium(II) is readily oxidised to higher oxidation states and therefore acts as a reducing agent capable of liberating hydrogen from dilute acids.

$\mathrm{Cr}^{2+}$: Chromium(II) is a very strong reducing agent and is easily oxidised to $\mathrm{Cr}^{3+}$; hence it liberates hydrogen from dilute acids.

$\mathrm{V}^{2+}$: Vanadium(II) is also a strong reducing agent and is oxidised to $\mathrm{V}^{3+}$, thereby liberating hydrogen.

Thus, all three ions listed can liberate hydrogen from a dilute acid.