Question

What is the oxidation number of phosphorus in the salt `Zr_3P_4O_16`?

Answer 1

Well, the parent phosphate ion is `PO_4^(3-)`...........

Explanation:

........And so the metal oxidation state would be `stackrel(+IV)M`.

And thus its perhalide formula would be `MX_4`, i.e. `M^(4+) + 4xxX^-`.

You might get a `"zirconium (IV) phosphate"`, you can certainly get `"zirconium tetrahalide"`.