\(Co = 6\);
\(O. N. = x + 5 \times (0) + 1 \times (-2) + 1\times (-1) = 0\)
\(\therefore \) \(x = + 3\) ; electronic configuration of
\(Co^{3+}[Ar]\, 3d^64s^0\) hence number of \(d\) electrons is \(6\). All \(d-\) electrons are paired due to strong ligand hence unpaired electron is zero.
(પરમાણુ ક્રમાંક : $Cr = 24, Mn = 25, Fe = 26, Co = 27$)
$(I)\, [CrCl_2(NO_2)_2(NH_3)_2]^-$ $(II)\, [Co(NO_2)_3(NH_3)_3]$
$(III)\, [PtCl(NO_2)(NH_3 )(py)]$ $(IV)\, [PtBrCl(en)]$
$(I)\,\,\,-\,\,\,(II)\,\,\,-\,\,\,(III)\,\,\,-\,\,\,(IV)$