Calculate number of atoms of aluminum of aluminum oxide with a mass of 2.3 Grams?

Molar mass of Al₂O₃ = 27.0×2 + 16.0×3 = 102.0 g/mol
Moles of Al₂O₃ = (2.3 g) / (102.0 g/mol) = 0.0225 mol

Each mole of Al₂O₃ contains 2 moles of Al atoms.
Moles of Al atoms = (0.0225 mol) × 2 = 0.045 mol

Avogadro constant = 6.02 × 10²³ /mol
No. of Al atoms = (0.045 mol) × (6.02 × 10²³ /mol) = 2.7 × 10⁻²²
(to 2 sig. fig.)

====
OR:
(2.3 g Al₂O₃) × (1 mol Al₂O₃ / 102.0 g Al₂O₃) × (2 mol Al / 1 mol Al₂O₃) × (6.02 × 10²³ Al atoms / 1 mol Al atoms)
= 2.7 × 10²² Al atoms
(to 2 sig. fig.)

(2.3 g Al2O3) / (101.96128 g Al2O3/mol) × (2 mol Al / 1 mol Al2O3) ×
(6.022 × 10^23 atoms/mol) = 2.7 × 10^22 atoms Al