According to Drago's rule lone pair on phosphorus resides in almost pure s-orbital, hence due to non-directionalnature, its overlapping tendency is greatly reduced in comparison to a lone pair present in hybrid orbital, which is directional as present in $\overset{\,\,\centerdot \,\,\centerdot \,\,\,\,\,\,\,\,}{\mathop{\text{N}{{\text{H}}_{3}}}}\,$.
$(I)$ આયનીકરણ ઉર્જા $(II)$ આયનીય ત્રિજ્યા
$(III)$ $X_2$ ની બંધ ઉર્જા $(IV)$બાષ્પીભવન એનથાલ્પી
$A, B$ અને $C$ શું હશે ?