Answer: option c. 3.6%
Step-by-step explanation:
1) Definition (formula)
Percent composition = (mass of solute / mass of solution) × 100.
2) Mass of solution = mass of seawater = 520 g.
3) Mass of solute
a) mass = molar mass × number of moles
b) The molar mass of NaCl may be calculated using the atomic masses of the elements given in a periodic table: 22.990 g/mol + 35.453 g/mol = 58.443 g/mol
c) mass of NaCl = 58.443 g/mol × 0.317 mol = 18.53 g.
d) Percent composition = (18.53 g / 520 g) × 100 = 3.6% ← answer