1. The problem statement, all variables and given/known data Sodium chlorate(I) Sodium chlorate(V) Potassium nitride(III) Phosphorus(III) chloride Magnesium iodate(I) 2. Relevant equations None 3. The attempt at a solution I know the number in the bracket refers to what's before it, i.e. in sodium chlorate(V), the (V) means that the chlorine has an oxidation number of +5, but how does this help me find the fomula of the copound. For example with sodium chlorate(V): I know its made from sodium (Na+) ions, and chlorate(ClO3-) ions.