The ones on left are the reactants
The elements heavier than hydrogen and helium were produced inside stars.
During most of a star's lifetime, hydrogen nuclei fuse together to form helium nuclei.As the star runs out of hydrogen, other elements. Heavier elements than hydrogen and helium are form. Elements heavier than iron are formed in supernovas.
All chemical reactions follow the law of conservation of mass. This means that the number of atoms of a specie before the reaction must equal to the number of atoms of that specie after that reaction. The only change that occurs in chemical reactions is the breaking and formation of chemical bonds, due to which energy may be released or absorbed.
A or c probably I think a tho