Identify the product 'B' obtained in following reaction.

$\mathrm{R}-\mathrm{C} \equiv \mathrm{N} \xrightarrow[\mathrm{HCl}]{\mathrm{SnCl}_2}\mathrm{A} \xrightarrow{\mathrm{H}_3 \mathrm{O}^{+}} \mathrm{B}$

Which of the following is radius of first orbit of He$^+$ ?

Identify heteroleptic complex from following.

Calculate rate constant of first order reaction if concentration of reactant decreases by $90 \%$ in 30 minute?