Why does PCI_3 fume in moisture?

Why does PCl_3 fume in moisture ?

Account for the following: PCl_3 fumes in moist air.

Why does NO_2 dimerise ?

Why does NO_2 dimerise ?

Why does NH_3 form hydrogen bond but PH_3 does not?

Why does NH_3 form hydrogen bonds but PH_3 does not ?

A wet porous subtance in the open air loses its moisture at a rate proportional to the moisture content. If a sheet hung in the wind loses half its moisture during the first hour, then the time when it would have lost 99.9% of its moisture is (weather conditions remaining same)