${~K}_{{d}}=\frac{1}{{k}_{{f}}}=4.7 \times 10^{-14}$
$\therefore {y}=4.7 \approx 5$
$(I)$ $K[Co(NH_3)_2(NO_2)_4$ $(II)$ $[Cr(NH_3)_3(NO_2)_3]$ $(III)$ $[Cr(NH_3)_5NO_2]_3[CO(NO_2)_6]_2$ $(IV)$ $Mg[Cr(NH_3) (NO_2)_5]$