# What is the correct name for the compound with the formula CrPO_4?

Since the oxidation states of $P$ can be $+ 3 \mathmr{and} + 5$, (and here it is obviously $+ 5$), and the oxidation state of $O$ is $- 2$ the total charge of the phosphate will be $- 3$, or $P {O}_{4}^{3 -}$
It is called phosphate because of this higher state (otherwise it would be called phosphite and be $P {O}_{3}^{3 +}$).
To compensate the chromium must have an oxidation state of $+ 3$, or $C {r}^{3 +}$, that's where the Lation $I I I$ comes in (because $C r$ kan have many different oxidation numbers, up to $+ 7$).