The maximum number of phases of a single substance which can coexist in equilibrium is two.

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According to the Gibbs phase rule, the maximum number of phases that can coexist in equilibrium for a single-component system is three. This is represented by the formula P + F = C + 2, where P is the number of phases, F is the degrees of freedom, and C is the number of components. For a single-component system (C = 1), if we have zero degrees of freedom (F = 0, meaning temperature and pressure are fixed), then P can be a maximum of 3. This is observed at the triple point where solid, liquid, and gas phases coexist in equilibrium.

The Maximum Number of Phases of a Single Substance Which