When the oxidation number of an element decreases over the course of a reaction, that element has beenwhich of the following chemical reactions is an oxidation-reduction reaction? cuso4 + bacl2 yields baso4 + cucl2 agno3 + nacl yields agcl + nano3 pb(no3)2 + 2nacl yields pbcl2 + 2nano3 zn + h2so4 yields znso4 + h2

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 !