Answer is: Four hydrogen nuclei join to form a helium nucleus, two neutrinos, and energy.
Hydrogen fusion cycle involves four hydrogen nuclei and two electrons and form of helium nucleus, two neutrinos and six photons.
This process occurs in three steps:
1) Fusion of hydrogen into deuterium.
2) The the formation of helium-3.
3) Recombination of two helium-3 into one nucleus of helium.
This fusion nuclear reaction is in the inner core of the Sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).