The valency of aluminium is 3. Write the valency of their radicals present in the following compounds.
(a) Aluminium chloride
(b) Aluminium oxide
(c) Aluminium nitride
(d) Aluminium sulphate
(a) Aluminium chloride = 1
(b) Aluminium oxide = 2
(c) Aluminium nitride = 3
(d) Aluminium sulphate = 2