Question

The point at which the solid, liquid, and gaseous forms of a substance co-exist is called the

• A. sublimation point
• B. distillation point
• C. triple point
• D. melting point

Hint:

Only the triple point involves all three phases together; melting and sublimation involve just two.

Answer 1

The Correct Option is C

This is a basic physical chemistry definition question, so matching the term to the description is enough.

1. Sublimation point: Describes solid turning straight to gas, involving only two phases.
2. Distillation point: Not a real phase-diagram term; distillation is a purification technique based on boiling points.
3. Triple point: The unique temperature and pressure combination where solid, liquid, and vapour phases of a substance are all in equilibrium together, exactly matching the question.
4. Melting point: Involves only the solid-to-liquid transition, missing the gas phase.

So the correct answer is option C, triple point.