A reaction of cobalt ( III ) chloride and ethylenediamine in a 1   :   2 mole ratio generates two…

The coordination number of cobalt is $6$.

The mole ratio of ${\mathrm{CoCl}}_3$ and $\mathrm{en}$ is $1 : 2$.

Hence,

${\mathrm{CoCl}}_3+2 \mathrm{en}\to \left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]\mathrm{ }\mathrm{Cl}$

The complex formed shows geometrical isomerism.

The complex exists as cis and trans isomers among which the trans isomer is optically inactive.