Question

when are parts per million and parts per billion used as measurements? when measuring concentrations that are exactly 50% when measuring concentrations that are smaller than 1% when measuring concentrations that are larger than 100% when measuring concentrations that exceed 10%

Explanation:

Parts per million (ppm) and parts per billion (ppb) are used for very small concentrations. A percentage is a part per hundred. 1% is 10000 ppm. So, ppm and ppb are used when concentrations are smaller than 1%.

Answer:

when measuring concentrations that are smaller than 1%