Work out the formulae for the following compounds :(a) Sodium oxide(b) Calcium carbonate

(a) Valency of Sodium = 1

Valency of Oxygen = 2

Formula for sodium oxide can be worked out by crossing the valency of the constituent elements.

Therefore, formula for sodium oxide is: Na₂O.

(b) Valency of Calcium      = 2

Valency of Carbonate ion = −2

Formula for calcium carbonate can be worked out by crossing  the valency of the constituent elements/ions.

Therefore, formula for calcium carbonate is: CaCO₃.