Answer
(a) \[~Fe,\text{ }Sc\]
(b) \[~Mn\]
(c) \[Ti\]
Work Step by Step
(a) The first-row transition metals that have \[+3\] as the highest possible oxidation state are as follows:
\[\begin{align}
& Fe:\quad \left[ Ar \right]3{{d}^{6}}4{{s}^{2}};\quad \quad F{{e}^{3+}}:\quad \left[ Ar \right]3{{d}^{5}} \\
& Sc:\quad \left[ Ar \right]3{{d}^{1}}4{{s}^{2}};\quad \quad S{{c}^{3+}}:\quad \left[ Ar \right] \\
\end{align}\]
(b) The first-row transition metal that has \[+7\] as the highest possible oxidation state is as follows:
\[Mn:\quad \left[ Ar \right]3{{d}^{2}}4{{s}^{2}};\quad \quad M{{n}^{7+}}:\quad \left[ Ar \right]\]
(c) The first-row transition metal that has \[+4\] as the highest possible oxidation state is as follows:
\[Ti:\quad \left[ Ar \right]3{{d}^{2}}4{{s}^{2}};\quad \quad T{{i}^{4+}}:\quad \left[ Ar \right]\]
