What does the pH scale measure?

The pH scale specifically measures the acidity or alkalinity of a solution. It is a logarithmic scale ranging from 0 to 14, where a value less than 7 indicates acidity, a value of 7 represents neutrality, and a value greater than 7 indicates alkalinity. This scale reflects the concentration of hydrogen ions (H⁺) in the solution; higher concentrations of H⁺ lead to lower pH values (more acidic), while lower concentrations result in higher pH values (more alkaline). This measurement is critical in many biological processes, as enzymes and metabolic activities are often pH-dependent, affecting functions such as nutrient availability and biochemical reactions.

Other choices such as temperature, concentration of salts, and presence of heavy metals pertain to different chemical properties and do not reflect the specific role of the pH scale. Temperature is measured in degrees, salts are quantified in molarity or concentration, and heavy metals are detected through various analytical methods, none of which pertain directly to what the pH scale provides.