[elt2112]

Would anyone be able to explain this to me please, I understand the phase rule is
F = C - P + 2
where F is degrees of freedom
C is number of compounds
P is number of phases in thermodynamic equilibrium
But I don't understand how this relates to the partial pressure and how I can sketch this?

[mjc123]

C is number of compounds

C is the number of components. Do you understand the difference? How many components are there in this system?
Assuming one degree of freedom is fixed (T = 1000°C), how many degrees of freedom are there for P_O2 to vary in each region of the diagram?

[unsu]

In the "Temperature - mole ratio" two-component phase diagrams the pressure is considered to be fixed (must be specified), so the phase rule is reduced to F = C - P + 1

If you add pressure, it is going to be a three dimensional diagram and you use F = C - P + 2

[mjc123]

The question asks you to fix the temperature and sketch pressure vs. mole ratio, so again F = C - P + 1