Question

Assertion:Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
Reason:Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substances.
A.Both Assertion and Reason are true and Reason is a correct explanation for assertion.
B.Both Assertion and Reason are true but Reason is NOT a correct explanation for assertion.
C.Assertion is true, reason is false.
D.Assertion is false, reason is true.

Answer 1

Hint:The process in which solid gets converted into gas without passing through the liquid phase is called sublimation. But the cause of this process is not evaporation. As evaporation is a process in which liquid gets converted into a gaseous phase. Both assertion and reasons are correct but reason is not the correct explanation for assertion.

Complete answer:
Sublimation is a process in which transition of phases takes place. In this process solid gets directly converted into gaseous phase without passing through the liquid phase. It is an endothermic process. It takes place when the temperature and pressure are below to its triple point in its phase diagram. Triple point corresponds to the lowest pressure at which the substance can exist as a liquid.
Evaporation is a type of vaporization that takes place on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be mixed with the evaporating substance. When the collision takes place between the molecules of the liquid, they transfer energy to each other that is based on the way they collide with each other.
It is true that sublimation is phase transition but evaporation is not the correct explanation for the sublimation process.

Hence, option B is correct.

Note:
There is a process in which a substance is converted directly from its gaseous phase to solid phase. This process is the reverse of sublimation. This process is called deposition or sublimation. But vaporization from liquid to gas occurs as evaporation from the surface if it occurs below the boiling point of the liquid, and as boiling with formation of bubbles in the interior of the liquid if it occurs at the boiling point, there is no such distinction for the solid-to-gas transition which always occurs as sublimation from the surface.