JEE Main · 2004 · 24 Apr 2004 · Offline · d and f Block Elements

The highest oxidation state a transition atom can reach is set by how many s and d electrons it can commit to bonding. The configuration $(n-1)d^{5}n{s}^2$ offers seven such electrons, and because the half-filled $d^5$ set is stable all seven can be used, supporting a $+7$ state just as manganese does in $\mathrm{MnO}{}_4{}^{-}$. None of the other configurations puts as many electrons within reach, so this one attains the highest oxidation state.