Which of the following complex species is not expected to exhibit optical isomerism?

• A

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

• B

  ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{+}$

• C

  $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]$

• D

  ${\left[\mathrm{Co}\left(\mathrm{en}\right)\left({\mathrm{NH}}_3\right){\mathrm{Cl}}_2\right]}^{+}$