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: $PF _3\,<\, PCl _3\,<\, PBr _3$