Which instrument measures pH and redox potential?

• A. Water level indicator
• B. pH/redox meters
• C. EC meters
• D. Gas detector

Answer: (B)

Measuring both pH and redox potential requires an instrument that combines sensors for hydrogen-ion activity and oxidation–reduction potential. A pH/redox meter is built for this, using a pH electrode (the glass electrode with a reference) to determine pH and an ORP electrode (usually platinum) to determine the redox potential, all read by a single meter. This allows you to monitor how acidic or basic a solution is while also gauging its tendency to gain or lose electrons, which reflects its oxidizing or reducing conditions. Together, these measurements provide a fuller picture of water chemistry, helping with processes like disinfection, corrosion control, and biological activity.

In contrast, the other tools listed don’t measure both properties: a water level indicator only tracks liquid height; a conductivity meter measures how well the solution conducts electricity (ions) but not pH or redox; and a gas detector measures gas concentrations, not aqueous pH or ORP.