What does the term pH measure in a solution?

The term pH specifically measures the level of acidity or basicity in a solution. It represents the concentration of hydrogen ions (H+) in the solution. A lower pH value indicates a higher concentration of hydrogen ions and thus greater acidity, while a higher pH value signifies a lower concentration of hydrogen ions and greater basicity (or alkalinity). The pH scale typically ranges from 0 to 14, with 7 being neutral, below 7 being acidic, and above 7 being basic. Understanding pH is fundamental in various fields, including chemistry, biology, and pharmacology, because it influences chemical reactions, biological functions, and the stability and solubility of compounds.

The other options provided do not relate directly to what pH measures. Total dissolved solids refer to all solids found in water, temperature indicates thermal energy, and density describes mass per volume—all of which are distinct properties not indicative of the solution's acidity or basicity.