How much 25% stock solution and distilled water will you need to make 1 L of a 1:400 solution?

Step 1 is to convert the ratio 1:400 to a percentage (1 ÷ 400) × 100 1 ÷ 400 = 0.0025 0.0025 × 100 = 0.25 Result at this step = 0.25% Step 2 is to calculate the volume of stock solution needed using (C1 × V1 = C2 × V2) V1 = (C2 × V2) ÷ C1 (0.25 × 1000) ÷ 25 0.25 × 1000 = 250 250 ÷ 25 = 10 Result at this step = 10 mL Step 3 is to calculate the amount of water needed Water = Total volume - Stock volume 1000 - 10 = 990 Result at this step = 990 mL Answer: A