How many geometrical isomers are possible for the complex $[Ma_3b_3]^{\pm n}$?

Which of the following will not show geometrical isomerism?

Choose the correct code regarding the possible number of geometrical isomers exhibited by the following complexes:
$I. [CrCl_2(NO_2)_2(NH_3)_2]^-$
$II. [Co(NO_2)_3(NH_3)_3]$
$III. [PtCl(NO_2)(NH_3)(py)]$
$IV. [PtBrCl(en)]$
Select the correct sequence for $I - II - III - IV$.

Which of the following compounds does not exhibit optical isomerism? $(en = \text{ethylenediamine})$

What is the value of effective magnetic moment found in $+3$ oxidation state of Chromium $(Z=24)$ (in $BM$)?

How many geometrical isomers are shown by the complex $[Pt(NH_3)(NH_2OH)(H_2O)(Py)]^+$?