All three phases can exist in an equilibrium with one another at the __ of a substance

Triple point

Explanation:

Yes, all three phases can exist in an equilibrium with one another at the triple point of a substance.

In thermodynamics, the triple point of a substance is defined as the point at which all three phases of substance co-exist together at a particular pressure and temperature.

for example, the triple point of mercury occurs at a temperature of −38.83440 °C and a pressure of 0.2 mPa.

And for water it is 0.01 °C and 611.73 pascals.

you will get some clear idea after seeing the graph.

And critical point as you see in the graph is end point of phase equilibrium curve, mainly liquid-vapor equilibrium

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