d
\(+4\) is the most stable oxidation state of vanadium and titanium. Mn \(^{3+}\) is not stable. \(\mathrm{Mn}^{2+},\) rather than \(\mathrm{Mn}^{3+}\) is much more stable in aqueous solution. For chromium, \(+3\) oxidation state is most stable in aqueous solution.