What measurement indicates the concentration of hydrogen ions in a sample?

The measurement that indicates the concentration of hydrogen ions in a sample is pH. The pH scale quantifies how acidic or basic a solution is, with lower values indicating a higher concentration of hydrogen ions (H+) and greater acidity. In the pH scale, a value of 7 is considered neutral, while values below 7 indicate acidity and values above 7 indicate basicity. The relationship between pH and hydrogen ion concentration is logarithmic, meaning that each whole number change on the pH scale represents a tenfold change in H+ concentration. Therefore, understanding pH is crucial in many scientific fields, including biochemistry and environmental science, as it directly affects chemical reactions and biological processes.

Conductivity, osmolarity, and viscosity measure different properties of a solution: conductivity measures the ability of a solution to conduct electricity, osmolarity quantifies the total concentration of solute particles in a solution, and viscosity refers to a fluid's resistance to flow. Each of these does not specifically indicate hydrogen ion concentration.