# Given a metal phosphate, M_3(PO_4)_2, what salt would this metal from with sulfate ion?

The corresponding metal sulfate would be $M S {O}_{4}$...........
We gots ${M}_{3} {\left(P {O}_{4}\right)}_{2}$; now phosphate anion is formally $P {O}_{4}^{3 -}$, i.e. a salt of $\text{phosphoric acid}$, ${H}_{3} P {O}_{4}$. And in the given formula we have $2 \times P {O}_{4}^{3 -}$, a formal electronic charge of $- 6$. Clearly, to form a neutral salt, the three metal ions must have a combined formal charge of $+ 6$, and given this we have ${M}^{2 +}$ ions.......
And thus the salt the metal forms with sulfate anion would be 1:1, i.e. ${M}^{2 +} S {O}_{4}^{2 -}$.