In which of the following substances will hydrogen bonds be strongest?

The difference in the $B.P.$ of $H_2O$ $(100 \ ^oC)$ and $H_2S$ $(-42 \ ^oC)$ is explained by:

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

In which of the following compounds does hydrogen bonding occur?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Dipole-dipole interactions are the only non-covalent interactions resulting in hydrogen bond formation.
Reason $R$: Fluorine is the most electronegative element and hydrogen bonds in $HF$ are symmetrical.

The molecular interactions responsible for hydrogen bonding in $HF$ are: