WAEC Chemistry 2023 Paper

Concept:The number of moles of a substance is calculated by dividing the given mass by its molar mass.Explanation:Oxygen exists as diatomic molecules, so one molecule of $\mathrm{O}_2$ contains two oxygen atoms.The atomic mass of oxygen is $16.0\ \mathrm{g/mol}$.Therefore, the molar mass of $\mathrm{O}_2$ is $2 \times 16.0 = 32.0\ \mathrm{g/mol}$.Use the formula: moles $= \frac{\text{mass}}{\text{molar mass}}$.Substitute the given values: moles $= \frac{3.0\ \mathrm{g}}{32.0\ \mathrm{g/mol}}$.This gives: moles $= 0.09375\ \mathrm{mol}$.Among the options, $0.09375\ \mathrm{mol}$ is closest to $0.0930\ \mathrm{mol}$.Answer:The correct option is B. $0.0930$ moles.