$BO_3$ units in boric acid are linked by which type of bond?

Which of the following molecules are expected to exhibit intermolecular $H$-bonding?
$(I)$ Acetic acid $(II)$ $o$-nitrophenol $(III)$ $m$-nitrophenol $(IV)$ $o$-boric acid
Select the correct alternative.

Hydrogen bonding is not present in

Acetic acid exists as a dimer in benzene solution. This is due to

Assertion : Molar enthalpy of vaporisation of water is different from ethanol.
Reason : Water is more polar than ethanol.

The variation of the boiling points of the hydrogen halides is in the order $HF > HI > HBr > HCl$. What explains the higher boiling point of hydrogen fluoride?