The number of geometrical isomers of a planar complex $M_{abcd}$ is

Which complex among the following is most paramagnetic?

$A$ reaction of cobalt $(III)$ chloride and ethylenediamine in a $1:2$ mole ratio generates two isomeric products $A$ (violet coloured) and $B$ (green coloured). $A$ can show optical activity,but $B$ is optically inactive. What type of isomers do $A$ and $B$ represent?

The pair of complex compounds $[Cr(H_2O)_6]Cl_3$ and $[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O$ are an example of

The spin-only magnetic moment of $Ni^{2+}$ in an aqueous solution in Bohr magneton $(\mu_B)$ is .......

Which one of the following complexes exhibits chirality?