Consider the following statements.
I. \(\mathrm{Cs}^{+}\)ion is more highly hydrated than other alkali metal ions.
II. Among the alkali metals, only lithium forms a stable nitride by direct combination with nitrogen.
III. Among the alkali metals \(\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}\), the metal, \(\mathrm{Rb}\) has the highest melting point.
IV. Among the alkali metals \(\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}\), only \(\mathrm{Li}\) forms peroxide when heated with oxygen.
Select the correct statement is.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.