The low density of ice compared to water is due to

The maximum possible number of hydrogen bonds in which an $H_2O$ molecule can participate is

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

The hydrogen bonds in solid $HF$ can be best represented as:

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 intramolecular hydrogen bond is present in