$EAN\ of\ Ni = 28 - 0 + 4 \times 2 = 34$
$EAN\ of\ SC^3 = 21 - 3 + 6 \times 2 = 30$
$EAN\ of\ Fe^{2+} = 26 - 2 + 6 \times 2 = 36$
$EAN\ of\ CO^{3+} = 27 - 3 + 6 \times 2 = 36$
$(I)$ $K[Co(NH_3)_2(NO_2)_4$ $(II)$ $[Cr(NH_3)_3(NO_2)_3]$ $(III)$ $[Cr(NH_3)_5NO_2]_3[CO(NO_2)_6]_2$ $(IV)$ $Mg[Cr(NH_3) (NO_2)_5]$