When four protons collide to form helium, what fraction of the original mass of the protons is converted to energy?

0.7 %

Explanation:

In a star like the Sun, or of smaller mass, the most frequent chain of nuclear reactions constitutes the cycle called p-p (proton-proton). This cycle begins with the fusion of two hydrogen nuclei (two protons) into one of deuterium, with the emission of a positron (the positron is the antiparticle of the electron, it is a positive electron) and a neutrino.

In this reaction 0.7% of the mass of the protons of the initial state is converted into energy. This number, 0.7%, is huge compared to that of a chemical reaction (a combustion, for example), which is typically of the order of 0.000000001%. Deuterium can in turn be fused with another hydrogen, this with helium.

From an energy point of view, what happens as a result of all these reactions is that four hydrogen nuclei fuse together, producing one of helium, two positrons, 2 neutrinos and 24.68 MeV of kinetic energy.

it should have an internal chamber and two thermometers sticking out of the top. the internal chamber will also be closed off from the outside.