Question

the triple point of a substance is

a. the point at which the substance changes state at the same pressure, temperature, and volume
b. the point when the density of a substance changes to a solid, liquid, or vapor at standard conditions.
c. that point when the substance changes its specific gravity at the same pressure, temperature, and volume
d. the point where a substance can exist as a solid, liquid, or vapor at the same time at one specific pressure and temperature

Explanation:

The triple point is a specific thermodynamic state where all three common phases (solid, liquid, gas/vapor) of a substance coexist in equilibrium, defined by a unique pressure and temperature. Options A, B, and C contain incorrect descriptions of this concept.

Answer:

D. The point where a substance can exist as a solid, liquid, or vapor at the same time at one specific pressure and temperature