In a synthesis reaction, two or more reactants combine to form a single product. In the reaction you provided:
NaPO3 + CuO → ?
We can identify that we are combining sodium phosphite (NaPO3) and copper(II) oxide (CuO). The likely product would be a compound that includes sodium (Na), copper (Cu), phosphorus (P), and oxygen (O).
The most straightforward product from this reaction would be sodium copper phosphonate, which is represented as:
NaCuPO4
Therefore, the correct product of the reaction is: NaCuPO4.