JEE Main 17 March 2021 Shift 1 Solved Paper

At intersection point ∆G=0, which represents the equilibrium
point and sudden increase in slope is due to melting or boiling point of the metal oxide.
According to Gibb's free rule,
∆G=∆H−T∆S
where, ∆H= change in enthalpy ∆G‌‌=‌ change in Gibb's free energy ‌
∆S‌‌=‌ change in entropy ‌
We can see that ∆G is dependent on ∆S.
So, when the phase changes (s→I or I→ g) the entropy increases and hence, slope increases.