What is considered equivalent to one part per million (ppm)?

One part per million (ppm) is a unit of concentration that describes the amount of a substance in a million parts of a solution, often used in contexts involving very low concentrations. The correct answer states that one part per million is equivalent to one milligram per kilogram.

This relationship is grounded in the metric system. Since one kilogram is equal to one million milligrams, one milligram of a substance in one kilogram of solution means that the substance constitutes one part per million. This direct conversion emphasizes that ppm is often expressed in milligrams for a solution of water or similar density, allowing for easy calculations and application in various contexts, such as environmental science or chemical concentrations.

Understanding this equivalence is crucial, particularly in fields dealing with safety thresholds, environmental pollutants, and chemical testing, where precise measurements and an appreciation of scale can significantly impact health and safety regulations.