Question

In the graph, “ppm” stands for parts per million. A concentration of one ppm is a ratio of one part to one million parts. Concentrations can also be expressed as a percentage. Why do you believe scientists choose ppm over percentage in some cases?

Answer 1

Answer:

ppm (or ppmm) is used to measure the concentration of a contaminant in soils and sediments. In that case 1 ppm equals 1 mg of substance per kg of solid (mg/kg). ... This use of ppm tends to be phased out in favour of mg/l. ppm (or ppmV) is often used to describe concentrations of contaminants in air (as a volume fraction).

Explanation:

So, instead of using a percentage which isn't the best way to describe the concentration of a solution. It makes it more difficult, whereas ppm is a simpler way to describe the concentration.