What measurement is used to quantify radioactivity?

The correct measurement used to quantify radioactivity is expressed in counts per minute (CPM) or related units, depending on the context. When assessing radioactivity, the focus is on the detection of radioactive decay events over a given time. Counts per minute indicates how many radioactive decay events are detected by a radiation measurement device in one minute, providing a direct measure of the activity level of a radioactive source.

Counts per million is a similar concept, often utilized in the context of environmental monitoring, such as assessing the concentration of radioactive materials in a sample relative to non-radioactive substances. This measurement can help scientists understand the environmental impact or exposure risk but fundamentally relates back to counts, thus making it relevant in the assessment of radioactivity.

The other options do not pertain to measuring radioactivity. Meters per second measures speed, micrograms per liter is a concentration measurement for substances in liquid, and millivolts pertain to electrical potential. Therefore, in relation to quantifying radioactivity, counts per million appropriately reflects the activity levels associated with radiation detection.