When a reaction between magnesium and hydrochloric acid take place the mass of the reactants is more than the mass of the products. why would this occur?

Https://edu.rsc.org/resources/the-rate-of-reaction-of-magnesium-with-hydrochloric-acid/1916.article

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.