The valencies (or charges) of some of the ions are given below:

Ion Valency	Ion Valency
(Charge)	(Charge)
Sodium 1+	Nitrate 1-
ion	Ion
Copper 2+	Sulphide 2-
ion	ion

Using this information, write down the formulae of:

(i) Sodium sulphide

(ii) Copper nitrate