a
\({\left[\mathrm{V}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+} \rightarrow \mathrm{d}^2 \mathrm{sp}^3}\)

\({ }_{23} \mathrm{~V}:-[\mathrm{Ar}] 3 \mathrm{~d}^3 4 \mathrm{~s}^2\)

\(\mathrm{~V}^{+j}:-[\mathrm{Ar}] 3 \mathrm{~d}^2, \mathrm{n}=2 \text { (even number of unpaired e) }\)

\({\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} \rightarrow \mathrm{sp}^3 \mathrm{~d}^2}\)

\({ }_{24} \mathrm{Cr}:-[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{~s}^1\)

\(\left.\mathrm{Cr}^{+2}:-[\mathrm{Ar}] 3 \mathrm{~d}^4, \mathrm{n}=4 \text { (even number of unpaired } \mathrm{e}^{-}\right)\)

\({\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+} \rightarrow \mathrm{sp}^3 \mathrm{~d}^2}\)

\(\mathrm{Fe}^{3+}:-[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{~s}^0\)

\(\mathrm{n}=5 \text { (odd number of unpaired } \mathrm{e}^{-} \text {) }\)

\({\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+} \rightarrow \mathrm{sp}^3 \mathrm{~d}^2}\)

\(\mathrm{Ni}:-[\mathrm{Ar}] 3 \mathrm{~d}^8 4 \mathrm{~s}^2\)

\(\mathrm{Ni}^{+3}:-[\mathrm{Ar}] 3 \mathrm{~d}^7, \mathrm{n}=3 \text { (odd number of unpaired } \mathrm{e}^{-} \text {) }\)

\({\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} \rightarrow \mathrm{sp}^3 \mathrm{~d}^2}\)

\(\mathrm{Cu}:-[\mathrm{Ar}] 3 \mathrm{~d}^9 4 \mathrm{~s}^0\)

\(\mathrm{n}=1 \text { (odd number of unpaired } \mathrm{e}^{-} \text {) }\)