The changing of gas into a liquid on cooling is called.
Condensation
The explanation for the correct option :
(d) Condensation: The process in which a gas changes into a liquid on cooling.
The explanation for the incorrect option :
(a)Vaporisation: The conversion of a substance from the liquid or solid phase into the gaseous(vapour) phase.
(b) Freezing: The process in which a liquid changes into a solid.
(b)Melting: The process in which solid changes into a liquid.
Thus.option (d).i.e Condensation is the correct answer.