The number of sulfate ions : 2.2 x 10²³
Reaction
Al₂(SO₄)₃⇒2Al³⁺+3SO₄²⁻
mol Al₂(SO₄)₃(MW=342,15 g/mol) :
[tex]\tt \dfrac{41.65}{342.15}=0.122[/tex]
mol of sulfate ions (SO₄²⁻)
[tex]\tt 3\times 0.122=0.366[/tex]
1 mol = 6.02 x 10²³ particles (ions, molecules, atoms), so for 0.366 mol :
[tex]\tt 0.366\times 6.02\times 10^{23}=2.20\times 10^{23}[/tex]