What is the percent by mass of a solution that contains 25 g KNO3 in 400.0 g H2O?

Percent by mass is (mass of solute ÷ mass of solution) × 100. The solution’s total mass is 25 g + 400.0 g = 425.0 g, so (25 ÷ 425.0) × 100 ≈ 5.9%. The correct choice is 5.9%.

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