In ___________, a solid substance passes directly into its vapour on the application of heat.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Sublimation
Sublimation is the change of a solid directly into vapour on heating, without passing through the liquid state; on cooling, the vapour turns back into the solid.
Camphor, naphthalene, ammonium chloride and iodine sublime. That is why sublimation is used to separate such a substance from a mixture with a solid that does not sublime, for example ammonium chloride from common salt.