Work out the formulae for the following compounds:
(a) Sodium oxide
(b) Calcium carbonate
(a) The valency of sodium is 1 and that of oxide is -2. So according to the valencies of both the elements, the formula becomes Na2O.
(b) The valency of calcium is 2 and that of carbonate is -2. So according to the valencies of both the elements, the formula becomes CaCO3.