The changing of a liquid into gas on heating is called.
Boiling
The explanation for the correct option:
(b)Boiling: The process in which a liquid changes into a gas.
The explanation for the incorrect option:
(a)Melting: The process in which solid changes into a liquid.
(c)Vaporisation: It is the vaporisation of an element or compound is a phase transition from the liquid phase to vapour phase.
(d)Condensation: The process in which a gas changes into a liquid.
Thus option (b) is the correct i.e Boiling.