How many electrons are transferred during the formation of one molecule of al2o3?

Six electrons are transferred in the formation of Al₂O₃.

Explanation:

Aluminium metal and Oxygen react to form Al₂O₃ as,

2 Al + 3/2 O₂ → Al₂O₃

Oxidation number of Al on left hand side is zero, while than on right hand side in Al₂O₃ is + 3. Means it has lost 3 electrons per one atom and six electrons per two atoms. Also, the oxidation number of O at left hand side in O₂ is zero, while that in Al₂O₃ it is - 2 per atom and - 6 per 3 atoms.

So, two Al atoms have lost 6 electrons and 3 O atoms have gained six electrons.