Suppose you need to make the following two precipitates (by two different precipitation reactions): MgCO3 and Ca3(PO4)2. For each reaction, choose the reactants from the drop-down box in such a way that the precipitate you need to make is the only product that forms?

Synthesis of MgCO3
Synthesis of Ca3(PO4)2

The question is incomplete, the complete question is:

Suppose you need to make the following two precipitates (by two different precipitation reactions): MgCO3 and Ca3(PO4)2.

For each reaction, choose the reactants from the drop-down box in such a way that the precipitate you need to make is the only product that forms?

Options:

Ca(NO3)2 amd K2HPO4, CaCl2 and Na2C2O4, MgCl2 and Na2C2O4, Mg(NO3)2 and Na3PO4, MgCl2 and Na2CO3, Ca(NO3) and Na2CO3

To precipitate MgCO3, we react MgCl2 and Na2CO3

To precipitate Ca3(PO4)2 we react CaCl2 and Na3PO4

Explanation:

The question specifies that reactants must be chosen such that the precipitate is the only solid product of the reaction. The compounds chosen as reactants must have high solubility in water. Hence the selected choices of reactants to yield the specified products was based on consideration of the solubility of the individual reactants in water and the nature of products formed by the two reactants. All reactants chosen are highly soluble in water but form one insoluble reaction product after reaction.

the answer is either b or c