Respuesta :

2Al₂O₃ = 4Al + 3O₂

M(A₂O₃)=101.96 g/mol
m(Al₂O₃)=250 g

n(O₂)=3m(Al₂O₃)/{2M(Al₂O₃)}

n(O₂)=3*250/{2*101.96}=3.678 mol