Question

formula of metal oxide is MO then formula for its phosphate is​

Answer 1

Answer: $M_3(PO_4)_2$

Explanation:

For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.  

Here the given compound is $MO$ which is formed by combination of metal having an oxidation state of +2 and oxygen having an oxidation state of -2. The oxidation states are exchanged and written in simplest whole number ratios to give neutral $MO$.

Thus when metal phosphate is to be formed by combination of metal having an oxidation state of +2 and phosphate $PO_4^{3-}$ having an oxidation state of -3. The oxidation states are exchanged and written in simplest whole number ratios to give neutral $M_3(PO_4)_2$.