The hydrogen bond is not present in

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.

Select the compound from the following that will show intramolecular hydrogen bonding.

Compounds showing hydrogen bonding among $HF, NH_3, H_2S$ and $PH_3$ are

In which of the following is intramolecular $H$-bonding absent?

The pair likely to form the strongest hydrogen bonding is