Question

What is the point at which all the three phases of a system exist?

(a) Triple point

(b) Sublimation point

(c) Vapor point

(d) Eutectic point

The question was asked during an internship interview.

The above asked question is from Gibb’s Phase Rule topic in section Phase Rule of Engineering Chemistry I

Answer 1

The correct choice is (a) Triple point

Explanation: Since at the triple point, the degree of freedom is zero (that is invariant reaction takes place at that point), therefore according to phase rule, F=C-P+2. Substituting the known values, we get P=3 (all states).