The one that is not expected to show isomerism is:

$\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]$ is tetrahedral complex, therefore does not show geometrical and optical isomerism.

$\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]$ does not show structural isomerism

$\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+} \&\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]$ show geometrical isomerism

$\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}$ show optical isomerism