Which type of instrument is typically used for measuring pH levels?

The instrument typically used for measuring pH levels is the pH meter. This device is specifically designed to provide precise measurements of hydrogen ion concentration in solutions, which directly relates to the pH value. A pH meter consists of a probe that can sense the voltage produced by the solution, which correlates to the pH level, allowing for quick and accurate readings.

Other instruments listed, such as a hydrometer, are designed for measuring specific gravity or density of liquids, while an acid-base titrator is used for determining the concentration of an acid or base in a solution through titration, not directly measuring pH levels. Similarly, a conductivity probe measures the electrical conductivity of a solution, which is useful for other types of analyses but does not provide direct pH measurements. The specificity of the pH meter for measuring acidity or alkalinity makes it the most suitable choice for this application.