The valency of aluminium in Al2O3 compound is:

To determine the valency of aluminium in Al2O3 compound, we need to analyze the compound's chemical formula.

1. The chemical formula Al2O3 indicates that there are two aluminium atoms (Al) and three oxygen atoms (O) in the compound.

2. The valency of oxygen is typically 2-. This means that each oxygen atom in the compound has a charge of -2.

3. Since there are three oxygen atoms in Al2O3, the total negative charge contributed by oxygen is -6 (3 x -2).

4. To balance the overall charge of the compound, the total positive charge contributed by aluminium must be +6.

5. Since there are two aluminium atoms in Al2O3, each aluminium atom must have a valency of +3 to contribute a total positive charge of +6.

Therefore, the valency of aluminium in Al2O3 compound is +3.