Question

Number of aluminium ions in 2g of aluminium oxide

Answer 1

Let us compute the molar mass of the molecule first

Mass of Al = 27 AMU
Mass of O = 16 AMU
So mass of Al2O3 "molecule" = 2x27 + 3x16 = 102 AMU

So 1 mole of  ALUMINIUM OXIDE will weigh 102 g
1 mole of any pure substance contains Avogrado's number of molecules, that is 6.023x10^23.
Thus 0.051g of ALUMINIUM OXIDE will contain 6.023x(10^23)x.051/102 = 6.023x(10^20)/2 "molecules "

Each molecule contains two ions of aluminium.

So total no. Of ions in the given amount of substance =  2x6.023x(10^20)/2 = 6.023x10^20