CBSE Class 9 Answered

Gram molecular mass of Al₂O₃ = 2 x 27 + 3  x 16 =  102 g

One molecule of Al₂O₃ has   =     two  Al³⁺ ions

Multiplying both sides by N_A (Avogadro's number).

N_A molecules of Al₂O₃ has   =    2 x N_A  Al³⁺ ions

Since 1 mole of a molecule contains N_A molecules

1 mole of Al₂O₃ has   =  2 x N_A  Al³⁺ ions

Since the mass of 1 mole of a molecule is gram molecular  mass

GMM of   Al₂O₃ has    = 2 x 6.023 x 10²³  Al³⁺ions

102 g of   Al₂O₃ has    = 2 x 6.023 x 10²³  Al³⁺ions

 102 g of   Al₂O₃ has   = 12.046 x 10²³  Al³⁺ions