IS textbook question

In calssical physics, energy and matter are two distinct entities. Hence we have separately the Law of Conservation of Energy and the Law of Conservation of Matter.

Since the formulation of the Special Relativity by Eienstein in 1905 and his famous matter energy equivalence equation E=mc^2, energy can be produced, in theory, by conversion of mass.

What is going on in the sun is a nuclear fusion process in which lighter atoms are fused together to form heavier atoms, e.g. from hydrogen to helium. Since the final helium fusion product is of less mass than the original hydrogen atoms, energy is produced because there is a loss of mass.