We know that cobalt is given as and chlorate refers to a group of atoms with an overall negative charge, i.e.
So we know two chlorates is needed to combine with to give a neutral compound:
As for , the phosphate ion is also polyatomic like chlorate and has an overall charge of -3, i.e. .
Since only one chromium ion is needed to take out the charge, that must mean its ion has a charge of +3. So, the nomenclature for the compound must be chromium (III) phosphate.