Answer is: helium.
Nuclear reaction is in the inner core of the Sun and hydrogen is conveted into helium.
The inner core is the central region of the Sun and all solar energy is produced in the core by nuclear fusion.
The Sun interior is divided into three regions: the inner core, the radiative zone and the convection zone.
Helium (symbol: He) is an element with atomic number 2 (2 protons) and mass number 4 (2 neutrons; n° = 4 - 2 = 2).
