Which of the following complexes is diamagnetic?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The total number of geometrical isomers shown by $[Co(en)_2 Cl_2]^{+}$ complex ion is three.
Reason $R$: $[Co(en)_2 Cl_2]^{+}$ complex ion has an octahedral geometry.
In the light of the above statements,choose the most appropriate answer from the options given below:

The increasing order of magnetic moments for the following complexes is:
$I$. $[Fe(CN)_6]^{4-}$
$II$. $[Fe(CN)_6]^{3-}$
$III$. $[Cr(NH_3)_6]^{3+}$
$IV$. $[Ni(H_2O)_4]^{2+}$

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

An octahedral complex having molecular composition $Co \cdot 5NH_3 \cdot Cl \cdot SO_4$ has two isomers $A$ and $B$. The solution of $A$ gives a white precipitate with $AgNO_3$ solution and the solution of $B$ gives a white precipitate with $BaCl_2$ solution. The type of isomerism exhibited by the complex is,

Identify the incorrect match from the following: