Question

At the triple point of a pure substance, the number of degrees of freedom is

• A. $2$
• B. $1$
• C. $0$
• D. $3$

Answer 1

The correct option is C $0$

$\text{Gibb's phase rule:}$
$F+P=C+2$

Where, F= degree of freedom, P = no.of phases

C = no. of components

For pure substance, no. of components, C = 1

$\text{At triple point, no. of phases,}P=3$

$\therefore$ $F+3=1+2$

$\text{Degree of freedom,}F=0$

Points To Remember:
(i) On P-T diagram, triple point and circuit point both are points.

(ii) On P-V diagram, triple point is a line and critical poin is a point