The  number of oxygen   atoms  that are  in 4 Al₂O₃  are 12 atoms
 Explanation
- The subscript  in  a chemical formula indicate the  number  of atoms of element  immediately   before the subscript.
- coefficient  is the  number  in front  of  the formula  and tells  us how many molecules  of a given formula  are  present.
- Since 4Al₂O₃  has coefficient of 4   and the subscript   of O is 3  the number of O atoms =  4 x 3=12 atoms