The molar mass of water (H2O) is 18.02 g/mol. Yun has 0.025 mol of H2O for a laboratory experiment. How many grams of water does she have?

Use mass = amount in moles × molar mass. For 0.025 mol of water, 0.025 × 18.02 g/mol = 0.4505 g, which rounds to 0.45 g. Therefore, Yun has 0.45 g of water, choice B.

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