Answer: The correct answer is Option a.
Step-by-step explanation:
Sun is the only star in Our Solar system. The reaction which continuously happens in Sun is nuclear fusion reaction. Due to this reaction the temperature of Sun is very high.
Nuclear fusion reaction is defined as the reaction in which two or more lighter nuclei combines together to form heavier nuclei with release of high amounts of energy.
The primary element in Sun is hydrogen. The fusion reaction requires heat and pressure to begin.
The reactions which happen in Sun are:
Overall reaction for the above series of reactions is given by:

Hence, the correct answer is Option a.