Answer:
The chemical formula of aluminum sulfate is Al2(SO4)3.
The formula shows that there are 3 atoms of oxygen (O) in each molecule of Al2(SO4)3.
Number of molecules of Al2(SO4)3 = 3.5×1024
Number of O atoms in 1 molecule of Al2(SO4)3 = 3
Number of O atoms in 3.5×1024 molecules of Al2(SO4)3 = (3.5×1024) x 3
= 1.05×1025
Therefore, there are 1.05×1025 moles of O atoms in 3.5×1024 molecules of Al2(SO4)3.