Answer:
Triple point.
Step-by-step explanation:
The point in the phase diagram where all the three phases (solid, liquid and gas) exist together is known as triple point.
At triple point:
C= components = 1
P = phase = 3
Therefore degree of freedom will be:
F = C-P+2 = 1-3+2=0
Thus the degree of freedom is zero.
For example:
The triple point of water is at 0.0075 degree celsius and 4.58 mmHg pressure.