What is the formula of aluminium oxide? 

Al₂O₃

The correct answer is option 4. Al₂O₃.

The formula of aluminum oxide is \( Al_2O_3 \)

Aluminum oxide, also known as alumina, is a chemical compound with the formula \( Al_2O_3 \). It is a white or colorless solid that is commonly found in nature as various minerals, such as corundum and bauxite. Aluminum oxide is an important industrial material used in the production of aluminum metal, abrasives, ceramics, refractories, and catalysts.