Question

what term describes the balance between pressure and gravity in a star?

protostar collapse
supernova expanse
hydrostatic equilibrium
nebula balance

Explanation:

Hydrostatic equilibrium is the state where the inward gravitational force is balanced by the outward pressure force in a star. A protostar collapse is the formation stage of a star. A supernova is an explosion at the end - stage of a massive star. Nebula balance is not a standard term for this pressure - gravity balance.

Answer:

hydrostatic equilibrium