Answer:
To solve this problem, we can use the definition of percent concentration by mass:
percent concentration = (mass of solute ÷ mass of solution) x 100%
We know that the percent concentration of NaCl in the solution is 15% by mass, and we have a 500 gram sample of the solution. Let's assume that the mass of NaCl in the sample is x grams.
Using the percent concentration formula, we can write:
15% = (x ÷ 500) x 100%
Simplifying this equation, we get:
x = (15 ÷ 100) x 500 = 75 grams
Therefore, there are 75 grams of NaCl in a 500 gram sample of the solution.
The correct answer is c. 75 grams.