The purple color of $KMnO_4$ is due to which of the following?

The molar ionic conductances of the octahedral complexes:
$(I)$ $PtCl_4 \cdot 5NH_3$
$(II)$ $PtCl_4 \cdot 4NH_3$
$(III)$ $PtCl_4 \cdot 3NH_3$
$(IV)$ $PtCl_4 \cdot 2NH_3$
Follow the order $-$

Assertion : $[Al(H_2O)_6]^{3+}$ is a stronger acid than $[Mg(H_2O)_6]^{2+}$.
Reason : Size of $[Al(H_2O)_6]^{3+}$ is smaller than $[Mg(H_2O)_6]^{2+}$ and possesses more effective nuclear charge.

The active substance in Nessler's reagent used for the detection of ammonia is ..........

$A$ solution contains $2.675 \ g$ of $CoCl_3 \cdot 6NH_3$ $(M = 267.5 \ g/mol)$. When passed through a cation exchanger,the chloride ions liberated are treated with excess $AgNO_3$ to yield $4.78 \ g$ of $AgCl$ $(M = 143.5 \ g/mol)$. What is the formula of the coordination compound?

Amongst the following,the most stable complex is:
$(i)$ $[Fe(H_2O)_6]^{3+}$
$(ii)$ $[Fe(NH_3)_6]^{3+}$
$(iii)$ $[Fe(C_2O_4)_3]^{3-}$
$(iv)$ $[FeCl_6]^{3-}$