Iron reacts with oxygen in a chemical hand-warmer. how should this reaction be categorized?
as an exothermic process because it releases heat
as an endothermic process because it releases heat
as an exothermic process because it absorbs heat
as an endothermic process because it absorbs heat

I believe the correct answer would be last option. The reaction is categorized as an endothermic process since it absorbs heat. This type of reaction requires a supply of heat energy in order for the reaction to proceed. Without the heat energy, the activation energy would not be reached and no reaction can be seen.

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.