if there are 19 grams of oxygen in a sample of aluminum oxide . how many grams of aluminium are present

Molecular Formula of (Aluminum Oxide) is Al2O3

Since the Molar Mass of Oxygen Atom = 16

Number of Moles (Atom) = Mass (Atom) / Molar Mass (Atom)

So, Number of Moles (Oxygen O3 Atom) = 19 / (16 * 3)
= 19 / 48
= 0.40 gm/mole

Molar Ratio of (Oxygen O3 Atom) = 0.40:3
Molar Ratio of (Aluminum Al2 Atom) = 0.27:2

Since, Number of Moles (Atom) = Mass (Atom) / Molecular Mass (Atom)

So, Mass (Atom) = Molar Mass (Atom) * Number of Moles (Atom)
Mass (Aluminum Al2 Atom) = 0.27 * (27 * 3)
= 0.27 * 81
= 21.87 gm