Answer:
             1.8 mol of CuO
Solution:
The balanced chemical equation is as follow,
                               2 Cu₂O  +  O₂     →     4 CuO
According to equation,
                     2 moles of Cu₂O produced  =  4 moles of CuO
So,
          0.900 moles of Cu₂O will produce  =  X moles of CuO
Solving for X,
                     X  =  (0.900 mol × 4 mol) ÷ 2 mol
                     X  =  1.8 mol of CuO