(આણ્વિય નંબર . : $Sc = 21, Ti = 22, Ni = 28,$$ Cu = 29, Co = 27$)
\(\mathrm{Ti} \rightarrow[\mathrm{Ar}] 3 d^{2} 4 s^{2}, \mathrm{Ti}^{3+} \rightarrow[\mathrm{Ar}] 3 d^{1}\)
\(\mathrm{Ni} \rightarrow[\mathrm{Ar}] 3 d^{8} 4 s^{2}, \mathrm{Ni}^{2+} \rightarrow[\mathrm{Ar}] 3 d^{8}\)
\(\mathrm{Cu} \rightarrow[\mathrm{Ar}] 3 d^{10} 4 s^{1}, \mathrm{Cu}^{+} \rightarrow[\mathrm{Ar}] 3 d^{10}\)
\(\mathrm{Co} \rightarrow[\mathrm{Ar}] 3 d^{7} 4 s^{2}, \mathrm{Co}^{2+} \rightarrow[\mathrm{Ar}] 3 d^{2}\)
\(\mathrm{Ti}^{3+}, \mathrm{Ni}^{2+}\) and \(\mathrm{Co}^{2+}\) are coloured due to presence of unpaired electrons.
(આપેલ : પરમાણુ કમાંક : $Ti : 22, V : 23, Cr : 24, Co : 27$)