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

Step 1: Understanding the Concept.
On a substance's phase diagram, different combinations of temperature and pressure decide whether it exists as solid, liquid, or gas.

Step 2: Check the options.
Sublimation is the direct change from solid to gas, not a co-existence of all three states, so option A is wrong. Distillation is a separation process, not a phase-diagram point, so option B is wrong. Melting point is where solid and liquid co-exist only, not gas as well, so option D is wrong.

Step 3: Final Answer.
The specific temperature and pressure at which solid, liquid, and gas all exist together in equilibrium is called the triple point, so option C is correct.