$\begin{array} {ll}
\text{Element} & \text{Electron Configuration}\\
1.\; Zr & a.\;[Ar]3d^2 \\
2. \; V^{3+} & b.\; [Kr]5s^24d^2 \\
3. \;Mo^{3+} & c.\;[Kr]4d^2
\end{array}$
$\begin {array} {1 1} (1) \rightarrow a; \quad (2) \rightarrow b; \quad (3) \rightarrow c \\ (1) \rightarrow b; \quad (2) \rightarrow a; \quad (3) \rightarrow c \\ (1) \rightarrow b; \quad (2) \rightarrow c; \quad (3) \rightarrow a \\ (1) \rightarrow c; \quad (2) \rightarrow a; \quad (3) \rightarrow b\end {array}$
