$(a)$ Lewis acidity order : $SiF_4 < SiC_{4} < SiBr_4 < Sil_4$
$(b)$ Melting point : $NH_3 > SbH_3 > AsH_3 > PH_3$
$(c)$ Boiling point : $NH_3 > SbH_3 > AsH_3 > PH_3$
$(d)$ Dipole moment order : $NH_3 > SbH_3 > AsH_3 > PH_3$
$(b)$ $(T)$ ; $M . P .$ 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.
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