Question

According to the Gibbs Phase Rule (F = C - P + 2), at the triple point of a pure metal (e.g., where solid, liquid, and vapour coexist), the degrees of freedom F is

• A. 1 (P can be varied)
• B. 2 (Both T and P can be varied)
• C. 0 (neither T nor P can be varied)
• D. 3

Hint:

At a triple point, $F = 0$ (invariant).
Along a phase boundary line, $P = 2 \implies F = 1$ (univariant).
Inside a single-phase region, $P = 1 \implies F = 2$ (bivariant).

Answer 1

The Correct Option is C