a
\((a)\)  \((F)\); As the sixe of halogen atom increases crowding on \(Si\) atom will increase, hence, tendency of attack of Lewise base decreases

\((b)\)  \((T)\) ; \(M . P .\) of \(N H_{3}\) is highest due to intermolecular \(H\) -bonding in it .

Next lower \(M.P.\) will be of \(\mathrm{SbH}_{3}\) followed by \(AsH_3\) due to high mol. wt. of \(SbH_3\).

\((c)\)  \((F)\) ; \(M.P.\) and \(B.P.\) of increase from \(\mathrm{PH}_{3}\) to \(\mathrm{SbH}_{3}\) via \(\mathrm{AsH}_{3}\) due to increase in moL wt. \(\mathrm{NH}_{3}\) does no follow this trend due to inter molecular \(H-\) bonding.

Increasing \(B.P.\) order \(: \mathrm{PH}_{3}<\mathrm{AsH}_{3}<\mathrm{NH}_{3}<\mathrm{SbH}_{3}\)

\((d)\) \((T)\) ; Value of bond moment decreases.