Answer: The correct option is D radiation pressure.
Explanation: When gravitational force tries to collapse the star in itself, the radiation pressure coming from the gamma rays creates a force in the outward direction. This outward force hence creates equilibrium and as a result, the star remains in a stable condition.
The radiation pressure is due to the gamma rays. These rays are produced through the fusion reaction, taking place in the core of the star.
Hypothetically considering, if this radiation pressure is not present the star will eventually collapse due to its own gravity. This phenomenon is termed Gravitational Collapse.