How many oxygen atoms are there in 98.4g of oxygen gas?

Molar mass of O₂ = 16.0×2 = 32.0 g/mol
No. of moles of O₂ = (98.4 g) / (32.0 g/mol) = 3.075 mol

Each mole of O₂ contains 6.023 × 10²³ O₂ molecules.
No. of O₂ molecules = (3.075 mol) × (6.023 × 10²³ molecules/mol) = 1.85 × 10²⁴ molecules

Each O₂ molecules contains 2 O atoms
No. of O atoms = (1.85 × 10²⁴ molecules) × (2 atoms/molecule) = 3.70 × 10²⁴ atoms

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OR:
(98.4 g O₂) × (1 mol O₂ / 32.0 g O₂) × (6.023 × 10²³ O₂ molecules / 1 mol O₂) × (2 O atom / 1 O₂ molecule)
= 3.70 × 10²⁴ O atoms

(98.4 g O) / (15.99943 g O/mol) x (6.022 x 10^23 atoms/mol) = 3.70 × 10^24 atoms O