Molecular compounds are usually formed by the combination between:

A particle P has 18 electrons, 20 neutrons and 19 protons. This particle must be:

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

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

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