Preparation of potassium permanganate from $\mathrm{MnO}_2$ involves two step process in which the 1st step is a reaction with KOH and $\mathrm{KNO}_3$ to produce

Which one of the carbocations from the following is most stable?

The product $(\mathrm{A})$ formed in the following reaction sequence is

$\mathrm{K}_{\mathrm{sp}}$ for $\mathrm{Cr}(\mathrm{OH})_3$ is $1.6 \times 10^{-30}$. What is the molar solubility of this salt in water?