Answer:
(2) parts per million
Explanation:
Concentration of a solution can be expressed in terms of parts-per-million (ppm).
ppm is usually used in the context of measuring very small concentrations particularly the amount of contaminants. It represents 1 part of the contaminant in 100000 parts of the total.
It is expressed as:
1 ppm = 1 mg / L
1 ppm = 1 mg/ Kg