Question

In this figure, what does O denote?

(a) Melting point

(b) Boiling point

(c) Triple point

(d) Vaporization point

The question was posed to me in an internship interview.

My enquiry is from Phases and Phase Diagrams in section Constitution of Alloys and Phase Diagrams of Engineering Material & Metallurgy

Answer 1

Right choice is (c) Triple point

To explain I would say: This graph illustrates the pressure-temperature diagram for a one-component phase diagram of the H2O system. The point O is marked as the triple point, which is the point at which three phases exist at the same time.