Multiple choice

Concentrations of substances are often expressed as:

  1. parts per thousand

  2. parts per million

  3. parts per billion

  4. "Holy cow, that's a LOT!"

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Concentrations of trace substances, such as pollutants in water or chemicals in soil, are commonly measured in parts per million (ppm) to express very small ratios.