The formula for magnesium carbonate is MgCO₃
Now, Mg belongs to group IIA in the periodic table and is a divalent cation
Since the molecule, MgCO₃ is neutral, the corresponding charge on the carbonate anion should be -2
i.e. we have: Mg²⁺ and CO₃²⁻
Now in Ag₂CO₃ , Ag and CO₃ combine in the ratio 2:1
We know that the charge on carbonate ion is -2.
i.e. 2(Ag cation charge) + 1(CO3 anion charge) = 0
2(Ag cation) + 1(-2) = 0
Ag charge = 2/2 = +1
Therefore, charge on Ag cation = +1