What is the percent composition by mass of a 100-gram salt solution that contains 30 grams of salt?

• A. 1.5%
• B. 15%
• C. 0.30%
• D. 30%

Answer: (D)

Percent composition by mass is found by dividing the mass of the component by the total mass of the solution and multiplying by 100. Here, salt accounts for 30 g of the total 100 g of solution, so the mass percent of salt is (30 / 100) × 100% = 30%. The remaining 70 g is the solvent. So the salt’s percent composition by mass is 30%.