Thermal stability: \(HF\, >\, HCl\, > \,HBr \,> \,HI\)

The decrease in thermal stability is due to decrease in bond dissociation enthalpy.

\(\Delta_{\text {diss }} H :- HF \,>\, HCl\, > \,HBr \,>\, HI\)

Bond angle: \(NH _3\,>\, PH _3\,>\, AsH _3\)

Lewis basic character: \(PF _3\,<\, PCl _3\,<\, PBr _3\)