Which of the following compounds contains a hydrogen bond?

The molar enthalpy of vaporisation of acetone is less than that of water. Why?

The compound/s which will show significant intermolecular $H$-bonding is/are :
$(a)$ $o$-Nitrophenol
$(b)$ $N$-($4$-hydroxyphenyl)acetamide
$(c)$ $2,6$-di-tert-butylphenol

Orthophosphoric acid $(H_3PO_4)$ exhibits high viscosity due to:

Which of the following is the correct order of increasing enthalpy of vaporization for the given hydrides?

The correct order of increasing intermolecular hydrogen bond strength is .... .