What is the mass of a single water molecule (molar mass 18 g mol⁻¹)?
Correct answer D. 2.99 × 10⁻²³ g
Explanation
Mass of one molecule = molar mass ÷ Avogadro's number = 18 ÷ 6.02 × 10²³ = 2.99 × 10⁻²³ g. Multiplying instead of dividing gives 1.08 × 10²⁵ g.
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