A $250 kg$ sample of a dilute aqueous solution of an industrial effluent contains $0.45 g$ of fluoride ion. Express the concentration in parts per million by mass (ppm) to two decimal places.

Numerical answer type, answer in ppm, tolerance 0.01.

Answer: 1.8 ppm

ppm = \frac{mass of solute}{mass of solution} \times 1 0^{6} = \frac{0.45}{250 \times 1 0 ^{3}} \times 1 0^{6} = 1.80