Answer : The phenomenon called as Nuclear Fusion is observed in the sun's core or solar core, where 4 atoms of Hydrogen molecule combines to give two atoms of Helium. It is due to fusing of two Hydrogen atoms to form one Helium molecule. In the core of sun this fusion process occurs, changing of mass of Hydrogen atom into Helium releases lot of energy in the form of heat and light.
The reaction that occurs inside the solar core is given below;
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