The process of nuclear fusion in the sun requires very high temperature and very high pressure. Nuclear fusion is the process in which two atomic nuclei combine to form a single, heavier nucleus. In the sun, the high temperature is necessary to provide the kinetic energy required for the atomic nuclei to overcome their electrostatic repulsion and come close enough together for the strong nuclear force to take effect. This allows the fusion process to occur.

Additionally, the high pressure in the sun is necessary to confine the atomic nuclei closely together. This pressure is created by the massive gravitational force exerted by the sun`s enormous mass. The high pressure helps to counteract the tendency of the atomic nuclei to repel each other due to their positive charges, allowing them to come close enough together for fusion to occur.

Therefore, both very high temperature and very high pressure are required for nuclear fusion to take place in the sun.