In the chemical formula Al₂O₃, the number 3 represents the number of oxygen atoms present in each molecule of aluminum oxide.

Here's a breakdown:

* Al: This represents the element aluminum.

* ₂: This subscript indicates that there are two aluminum atoms in each molecule.

* O: This represents the element oxygen.

* ₃: This subscript indicates that there are three oxygen atoms in each molecule.

Therefore, the formula Al₂O₃ tells us that aluminum oxide is composed of two aluminum atoms and three oxygen atoms per molecule.