\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{-2} \to \mathrm{Cr}^{+6}\to\) dlamagnetic
\(\mathrm{MnO}_{4}^{-} \to \mathrm{Mn}^{+7}\to\) diamagnetic
\(\mathrm{MnO}_{4}^{-2}\to\mathrm{Mn}^{+6}\to\) paramagnetic
unpaired electron is present so \(d-d\) transition is possible
$(I)\, Pt(SCN)_2 - 3PEt_3,$ $(II)\,CoBr ·SO_4 · 5NH_3$ $(III)\, FeCl_2 · 6H_2O$
$\left( {{C_2}O_4^{2 - } = } \right.$ ઓક્ઝલેટો $)$