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Hydrogen burning
Four protons and two electrons become one ⁴He nucleus and two neutrinos, and 26.7 MeV (the positrons the branches make, two in most, one in pp-II where an electron is captured instead, annihilate with electrons of the plasma; that energy is counted). A star does it in two ways: the pp chains, built on the slow weak fusion of two protons, and the CNO cycle, where carbon, nitrogen and oxygen catch protons and give back an α. Each burns at its own pace; the slowest step sets it.