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

$26.7 \ g$ of a compound with the formula $PtCl_2Br_2 \cdot 6H_2O$ is taken for analysis. This compound exhibits stereoisomerism,and a total of $3$ stereoisomers exist. Find the loss in mass (in $g$) when the given amount of the compound is treated with concentrated $H_2SO_4$. (Molar mass: $PtCl_2Br_2 \cdot 6H_2O = 534 \ g \ mol^{-1}$)

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

The metal ion whose electronic configuration is not affected by the nature of the ligand and which gives a violet colour in non-luminous flame under hot condition in borax bead test is

How many geometrical isomers does $[Pt(NH_3)(Br)(Cl)(Py)]$ have?

Consider the following metal complexes:
$1. [Co(NH_3)_6]^{3+}$
$2. [CoCl(NH_3)_5]^{2+}$
$3. [Co(CN)_6]^{3-}$
$4. [Co(NH_3)_5(H_2O)]^{3+}$
The spin-only magnetic moment value of the complex that absorbs light with the shortest wavelength is $B.M.$ (Nearest integer).