The ability of an atom to bond with neighboring atoms and be involved in chemical reactions depends on thenumber of electrons in its outer (valence) shell. energy level of its electrons. number of protons plus the number of neutrons. total number of electron shells present in the atoms. number of electrons in relation to the number of neutrons.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

the answers would be

the first one and the second one