Explain the process of nuclear fusion in the Sun.

In the Sun the main fusion process is the fusion of hydrogen nuclei to form helium nuclei. Any two hydrogen nuclei repel each other as they are both positively charged, for the fusion to occur the two nuclei need to get close enough together so that this repulsion is overcome. This is achieved by the high temperature and pressure in the core of the Sun. The total mass of the products is less than the total mass of the reactants, the mass difference is released as energy, given by the equation E = mc².