What does an activity assay demonstrate?

• A. A compound is present and active.
• B. A compound is degraded.
• C. The assay measures color change only.
• D. The assay estimates molecular weight.

Answer: (A)

An activity assay is about function: it reveals whether a compound can perform its intended biological effect in a given system. A positive result means the compound is present and still active under the assay conditions, capable of producing the expected functional outcome (such as catalyzing a reaction or triggering a signal). It’s not just about being there or about a color change, since readouts can vary (luminescence, fluorescence, kinetics) and aren’t limited to color. It also isn’t a measure of molecular weight. So the best answer is that the assay demonstrates the compound is present and active.