The number of possible isomers for the complex $[Co(en)_2Cl_2]Cl$ will be (en = ethylenediamine):

The complex $[Co(en)_2Cl_2]Cl$ ionizes to give the coordination entity $[Co(en)_2Cl_2]^+$. This complex belongs to the type $[M(AA)_2a_2]$, where 'AA' is a symmetrical bidentate ligand ($en$) and 'a' is a monodentate ligand ($Cl^-$).

1. Geometrical Isomerism: The complex shows geometrical isomerism with two forms:

• Trans-isomer: The two $Cl^-$ ions are at 180° to each other. This structure has a plane of symmetry and is optically inactive (achiral).
• Cis-isomer: The two $Cl^-$ ions are at 90° to each other. This structure lacks a plane of symmetry and is optically active.

2. Optical Isomerism:

• The cis-isomer is chiral and exists as a pair of enantiomers (dextro and laevo forms).
• The trans-isomer is achiral and does not show optical isomerism.

Total Isomers: 1 (Trans) + 2 (Cis-d and Cis-l) = 3 isomers .