According to Modern Physics pages 488 and 489, the proton-proton chain is believed to be responsible for most the sun's energy. The proton-proton chain involves three different reactions
The reactions with labels (1) and (2) must each occur twice. Therefore, 6 s are required to produce 2 s along with an . Therefore, the proton-proton chain results in a net loss of 4 into a net gain of . Therefore, answer (B) is correct.