The relatively high boiling point of $HF$ is due to

Why does $NH_{3}$ form hydrogen bond but $PH_{3}$ does not?

The dominant intermolecular force that must be overcome to convert liquid methanol to its vapour is

The number of hydrogen bonds formed by a water molecule at normal conditions is

Viscosity of a liquid arises due to strong intermolecular forces existing between the molecules. Stronger the intermolecular forces,greater is the viscosity. Name the intermolecular forces existing in the following liquids and arrange them in the increasing order of their viscosities. Also give reason for the assigned order in one line.
Water,hexane $(CH_3CH_2CH_2CH_2CH_2CH_3)$,glycerine $(CH_2OHCH(OH)CH_2OH)$

The boiling points of $HF$,$HCl$,$HBr$ and $HI$ follow the order: