Which term refers to the measure of acidity or alkalinity of a substance?

The term that refers to the measure of acidity or alkalinity of a substance is pH. The pH scale ranges from 0 to 14, where a pH of 7 is considered neutral, values below 7 indicate acidity, and values above 7 indicate alkalinity. This measurement is vital in various fields, such as chemistry, biology, and environmental science, as it affects chemical reactions, biological processes, and the health of ecosystems. Understanding pH is crucial for tasks like balancing soil for agriculture, managing water quality in aquatic systems, and formulating products in industries such as pharmaceuticals and cosmetics.

Other terms from the choices provided relate to different scientific concepts. Oxidation refers to a chemical reaction involving the loss of electrons, viscosity describes a fluid's resistance to flow, and density measures mass per unit volume, none of which pertain directly to acidity or alkalinity. Thus, pH is the correct term to indicate the level of acidity or alkalinity in a substance.