Question

Given below are two statements: Statement I: Sublimation is a purification technique that is used to separate those solid substances which change from solid to vapour state without passing through liquid state. Statement II: If external atmospheric pressure is reduced, then boiling point of a substance is decreased. In the light of the above statements, choose the correct option.

• A. Both statement I and statement II are correct
• B. Both statement I and statement II are incorrect
• C. Statement I is correct but statement II is incorrect
• D. Statement I is incorrect but statement II is correct

Hint:

At high altitudes, water boils at a lower temperature due to reduced atmospheric pressure.

Answer 1

The Correct Option is A

Concept:

Sublimation is the direct conversion of a solid into vapour without passing through the liquid phase.
Boiling occurs when vapour pressure of a liquid equals external atmospheric pressure.
Step 1: Verification of Statement I. Certain solids like camphor, ammonium chloride, and naphthalene undergo sublimation. This property is used to purify such substances. \[ \Rightarrow \text{Statement I is correct.} \]
Step 2: Verification of Statement II. When external pressure is reduced, the vapour pressure equals atmospheric pressure at a lower temperature. \[ \Rightarrow \text{Boiling point decreases with decrease in pressure.} \] \[ \Rightarrow \text{Statement II is correct.} \] Conclusion: Both Statement I and Statement II are correct.