The number of geometrical isomers for $[Co(NH_3)_3(NO_2)_3]$ is ....

Given below are two statements:
Statement $I$: $A$ homoleptic octahedral complex,formed using monodentate ligands,will not show stereoisomerism.
Statement $II$: $cis-$ and $trans-$ platin are heteroleptic complexes of $Pd$.
In the light of the above statements,choose the correct answer from the options given below.

Which of the following exhibits coordination isomerism?

Which of the following exhibits optical isomerism? $(en = \text{ethylenediamine})$

Which of the following complexes is capable of showing optical isomerism?

The experimental value of the magnetic moment of a $Mn^{2+}$ complex is $5.96 \ BM$. This indicates that: