Answer: 108 g
Step-by-step explanation:
The molar mass of aluminium is 26.98 g/mol; the molar mass of (atomic) oxygen is 16.00 g/mol.
1 mole of Al₂O₃ therefore has a mass of 2(26.98) + 3(16.00) = 101.96 g.
Divide this into the given mass, to find the number of moles here:
(204 g)/(101.96 g/mol) = 2.001 mol.
There are 2 moles of aluminium per mole of aluminium oxide, so there are
2(2.001) = 4.002 moles of aluminium in the sample.
Then there are (4.002 mol)(26.98 g/mol) = 107.97 g of Al. Since the given mass has only 3 significant figures, round this answer to 108 g.