How many Aluminum ions are in 4.5 moles of aluminum oxide?

Hat means that 12 g of Al2
2
O3
3
contain 12 g / 101.96 g mol−1
−
1
= 0.118 moles of Al2
2
O3
3
.

Each Al2
2
O3
3
formula unit contains two Al3+
3
+
ions, so there are 2 x 0.118 mol = 0.235 moles of Al3+
3
+
ions.

If you want an actual number, you can multiply that by Avogadro’s constant: 0.235 mol x 6.022 x 1023
23
mol−1
−
1
= 1.42 x 1023
23
ions.