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MCQEasyJEE 2026Purification Methods (Crystallisation, Sublimation, Distillation)

JEE Chemistry 2026 Question with Solution

Given below are two statements :

Statement I: Sublimation is used for the separation and purification of compounds with low melting point.

Statement II: The boiling point of a liquid increases as the external pressure is reduced.

In the light of the above statements, choose the correct answer from the options given below :

  • A

    Both Statement I and Statement II are false

  • B

    Statement I is false but Statement II is true

  • C

    Statement I is true but Statement II is false

  • D

    Both Statement I and Statement II are true

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: Two statements about sublimation and boiling point are to be checked.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Statement I: Sublimation is used for separation and purification of solids that pass directly from solid to gas. This depends on the substance being sublimable, that is, having sufficiently high vapour pressure below its melting point. It is not identified merely by having a low melting point. Therefore, Statement I is false.

Statement II: A liquid boils when its vapour pressure becomes equal to the external pressure. If the external pressure is reduced, the liquid reaches this condition at a lower temperature. Therefore, the boiling point decreases, not increases. Hence, Statement II is false.

Therefore, both Statement I and Statement II are false, so the correct option is A.

Common mistakes

  • Assuming sublimation is determined only by low melting point is incorrect. A substance must vaporise directly from the solid state without becoming liquid under the given conditions. Focus on sublimable nature and vapour pressure, not only melting point.

  • Thinking that lowering external pressure increases boiling point reverses the actual relation. Boiling occurs when vapour pressure equals external pressure, so reducing external pressure makes boiling occur at a lower temperature.

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