First, we calculate the moles of Al₂(SO₄)₃:
moles = mass / Mr
= 4.4 / (27 x 2 + 3 x (32 + 16 x 4))
= 0.013 mole
Each mole of Al₂(SO₄)₃ contains 12 moles of Oxygen
Moles of oxygen = 12 x 0.013
= 0.156
Each mole of Oxygen contains 6.02 x 10²³ atoms
Atoms of Oxygen = 0.156 x 6.02 x 10²³
= 9.39 x 10²² atoms