The formula of a compound is X₃Y. The valencies of elements X and Y will be respectively:

An ionic compound will be formed by the combination of one of the following pairs of elements. This pair of elements is:

Molecular compounds are usually formed by the combination between:

The formula of the sulphate of an element X is X₂(SO₄)₃. The formula of nitride of element X will be:

An element A forms an oxide A₂O₅.

(a) What is the valency of element A?

(b) What will be the formula of chloride of A?