Based on the data given below, which metal in its +2 oxidation state…

The correct answer is Option (1) → Co

A metal ion in the +2 state liberates hydrogen from an acid only if it is a good reducing agent, that is, if it is easily oxidised to the +3 state while \( \ce{H+} \) is reduced to \( \ce{H2} \):

    \( \displaystyle \ce{2M^2+(aq) + 2H^+(aq) -> 2M^3+(aq) + H2(g)} \)

The standard potential \( E^\circ(\ce{M^3+}/\ce{M^2+}) \) tells which way the couple goes. A negative value means \( \ce{M^2+} \) gives up an electron more readily than \( \ce{H2} \) does (\( E^\circ = 0 \) for \( \ce{H+}/\ce{H2} \)), so \( \ce{M^2+} \) reduces \( \ce{H+} \). A large positive value means \( \ce{M^3+} \) is a strong oxidising agent and \( \ce{M^2+} \) is the stable state, which does not reduce \( \ce{H+} \).

• V (−0.26 V), Ti (−0.37 V) and Cr (−0.41 V): \( \ce{V^2+} \), \( \ce{Ti^2+} \) and \( \ce{Cr^2+} \) are strong reducing agents and liberate hydrogen, for example \( \ce{2Cr^2+ + 2H^+ -> 2Cr^3+ + H2} \).

• Co (+1.97 V): \( \ce{Co^3+} \) is one of the strongest oxidising agents in water, so \( \ce{Co^2+} \) has no tendency to be oxidised and does not liberate hydrogen.

So the metal is cobalt.

NCERT (2026-27 edition):
Chemical Reactivity and E^o Values – …