A solution is provided as 1 g/10 mL. How many milliliters are needed to obtain 0.5 g?

• A. 0.5 mL.
• B. 50 mL.
• C. 10 mL.
• D. 5 mL.

Answer: (D)

Understanding how concentration works: a fixed concentration means the amount of solute is directly proportional to the volume of solution. Here, 1 g is in 10 mL, so the solution contains 0.1 g per mL. To obtain 0.5 g, divide by the concentration: 0.5 g ÷ 0.1 g/mL = 5 mL. So 5 mL of the solution provides 0.5 g of solute.

Quick checks show other volumes wouldn’t give 0.5 g: 0.5 mL would have 0.05 g, 10 mL would have 1 g, and 50 mL would have 5 g. Only 5 mL yields the desired 0.5 g.