Answer: 1. Two protons within the Sun fuse. Most of the time the pair breaks apart again, but sometimes one of the protons transforms into 2.a neutron via a weak nuclear force. Along with the transformation into a neutron, a positron, and neutrino are formed. This resulting proton-neutron pair that forms sometimes is known as deuterium.
3. A third proton collides with the formed deuterium. This collision results in the formation of a helium-3 nucleus and a gamma ray. These gamma rays work their way out from the core of the Sun and are released as sunlight.
4Two helium-3 nuclei collide, creating a helium-4 nucleus plus two extra protons that escape as two hydrogens. Technically, beryllium-6 nuclei form first but are unstable and thus disintegrate into the helium-4 nucleus.
Explanation:
The final helium-4 atom has less mass than the original 4 protons that came together (see E=mc2). Because of this, their combination results in an excess of energy being released in the form of heat and light that exits the Sun, given by the mass-energy equivalence. To exit the Sun, this energy must travel through many layers to the photosphere before it can emerge into space as sunlight. Since this proton-proton chain happens frequently - 9.2 x 1037 times per second - there is a significant release of energy.[3] Of all of the mass that undergoes this fusion process, only about 0.7% of it is turned into energy. Although this seems like a small amount of mass, this is equal to 4.26 million metric tonnes of matter being converted to energy per second.[3] Using the mass-energy equivalence, we find that these 4.26 million metric tonnes of matter are equal to about 3.8 x 1026 joules of energy released per second!