Which instrument is used to measure pH?

• A. Turbidity meter
• B. Electrometric meter
• C. Conductivity meter
• D. Thermometer

Answer: (B)

Measuring pH relies on detecting the electrical potential produced by hydrogen ion activity in the solution. An electrometric instrument is designed to measure those electrical potentials and translate them into a pH reading. In practice, a pH meter uses a glass electrode sensitive to H+ ions and a reference electrode; the meter converts the voltage difference into a pH value after calibration with standard buffer solutions. This direct link between ion activity and a readable pH scale is why an electrometric meter is the appropriate tool. Other devices measure different properties: a turbidity meter gauges cloudiness with light, a conductivity meter assesses how well the solution conducts electricity, and a thermometer measures temperature. These do not directly measure hydrogen ion activity, so they aren’t used to determine pH.