The formula of Aluminium sulphide: 

The chemical formula for aluminium sulphide, often known as aluminium sulphide, is ${\text{Al}}_2{\text{S}}_3$. In the air, it easily hydrolyzes to produce hydrogen sulphide. Aluminium sulphide is a substance that is greyish in colour and smells strongly of sulphur. It comes in six different crystalline forms: α, β, γ and δ. It can be created by combining sulphur and aluminium particles in a thermite-like process.

Aluminium in its ionic state shows +3 oxidation number and sulphide ion has -2 oxidation state. Thus two aluminium and three sulphide ions are bonded to form aluminium sulphide. Therefore the correct answer is ${\text{Al}}_2{\text{S}}_3$.

Hence, option D is correct.