Which of the following isomerism is exhibited by $[CrCl_2(OH)_2(NH_3)_2]^-$?

The electronic configurations of $Cr^{2+}$,$Mn^{2+}$,$Fe^{2+}$,and $Co^{2+}$ ions are $d^4$,$d^5$,$d^6$,and $d^7$ respectively. Which of the following complexes has the minimum paramagnetic character?

The formula for calculating 'spin only' magnetic moment is

Which of the following complexes will exhibit the highest number of isomers?

Select the diamagnetic coloured compound:

$A$ complex compound which can show optical isomerism but not geometrical isomerism is: