What does pH measure?

pH specifically measures the concentration of hydrogen ions in a solution. It is a logarithmic scale that reflects how acidic or basic a solution is, with lower pH values indicating high acidity (more hydrogen ions) and higher pH values indicating basicity (fewer hydrogen ions). A neutral solution, such as pure water, has a pH of around 7, where the concentration of hydrogen ions is equal to that of hydroxide ions.

The concept of pH is central to many scientific fields, including chemistry, biology, and environmental science because the pH level can significantly influence chemical reactions, biological processes, and the solubility of various substances. Understanding hydrogen ion concentration is crucial for applications ranging from physiological processes in living organisms to the behavior of pollutants in natural waters.

Oxygen levels, carbon dioxide levels, and electronegativity measure different aspects entirely. While they are important in their respective contexts, they do not relate to the measure of pH or hydrogen ions in a solution. The focus on hydrogen concentration makes the first choice the correct one for this question.