Select correct statement :

• A

  Geometrical isomers of complexes may differ in dipole moment and visible / UV spectra
• B

  Complexes of the type $\left[{\text{Ma}}_3{\text{b}}_3\right]$ can also have facial (fac) and meridional (mer) isomer
• C

  No optical isomer exists for the complex trans - ${\left[\text{Co}{\left(\text{en}\right)}_2{\text{Cl}}_2\right]}^{+}$
• Correct answer
  D

  All are correct

Hence, the correct answer is option: 'D'.