Answer:
Ca(NO3)2 + Na2CO3 -> CaCO3 + 2NaNO3
Step-by-step explanation:
As Calcium ion (Ca) has a valency of +2, it requires an anion with equivalent valency of -2. Nitrate ion (NO3) has a valency of -1 so it needs 2 molecules of it to satisfy the Calcium's +2 valency.
Carbonate (CO3) has -2 valency, so it replaces the 2 NO3 molecules by 1 of itself and bonds to Ca.
Sodium (Na) has +1 valency, so it is satisfied by 1 molecule of NO3 but there are 2 molecules of both Na and NO3. Therefore, we attach the stoichiometric coefficient of 2 to NaNO3.