$A$ complex of the type $[M(AA)_{2}X_{2}]^{n+}$ is known to be optically active. What does this indicate about the structure of the complex? Give one example of such a complex.

(N/A) The fact that the complex $[M(AA)_{2}X_{2}]^{n+}$ is optically active indicates that it must exist in the $cis$-form,which lacks a plane of symmetry and is therefore chiral (asymmetric).
For example: $[Co(en)_{2}Cl_{2}]^{+}$ is an optically active complex where $en$ is ethylenediamine ($AA$ type ligand) and $Cl$ is the $X$ type ligand.
The $trans$-isomer of this complex is optically inactive because it possesses a plane of symmetry.