Which one of the following reactions is the main cause of the energy radiation from the Sun ?

The primary source of energy radiation from the Sun is nuclear fusion [1]. In the Sun's core, extreme temperatures (approximately 15 million degrees Celsius) and immense pressure allow hydrogen nuclei to overcome electrostatic repulsion and collide [4]. This process, predominantly occurring via the proton-proton (pp) chain reaction, involves the fusion of hydrogen atoms into helium [3]. During this reaction, a small amount of mass is converted into a tremendous amount of energy, as described by Einstein's mass-energy equivalence principle, E=mc² [4]. While stars larger than the Sun may utilize the CNO cycle, the proton-proton chain remains the dominant fusion process for the Sun [4]. Unlike fission, which involves splitting heavy nuclei, or chemical reactions which involve electron interactions, fusion involves the joining of light nuclei to release energy.

Sources

1. [1] https://www.sciencedirect.com/topics/engineering/fusion-reaction
2. [4] https://www.energy.gov/science/doe-explainsfusion-reactions
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Protostar > p. 9