a: 1 b:2 c:1 d:1 You just have to make sure that there are the same amounts of each element on each side. So for this one because there are two Cl in the reactant the HCl compound needs to be balanced with a two and also there are two H in the products so you need to make sure the HCl compound has a two in front of it so that it is balanced. Everything else has one on each side so now balance is needed. You put 1 in when there is no balance number needed.
