A gas cylinder contains exactly 1 mole of oxygen gas (O2). How many molecules of oxygen are in the cylinder?

One mole of any substance contains Avogadro’s number of particles, approximately 6.02 × 10²³. For oxygen gas, those particles are O₂ molecules, so 1 mole contains 6.02 × 10²³ molecules. The correct choice is B, 6.02 × 10²³ molecules.

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