What does the pH scale primarily measure?

The pH scale primarily measures the degree of acidity or alkalinity of a solution. It quantifies the concentration of hydrogen ions (H+) in a solution, with lower pH values indicating a higher concentration of hydrogen ions and thus a more acidic solution, while higher pH values indicate a lower concentration of hydrogen ions and a more alkaline solution. The scale typically ranges from 0 to 14, where 7 is considered neutral. Understanding the pH level is crucial in various fields such as chemistry, biology, and even in skincare and cosmetics, as it affects the stability and reactivity of substances.

The other options relate to different physical properties of solutions: temperature refers to the thermal energy, electrical conductivity involves how well a solution can conduct electricity, and viscosity measures a liquid's resistance to flow. None of these properties are assessed by the pH scale, which is exclusively focused on acidity and alkalinity.