Which unit is used to express turbidity in the context described?

• A. Nephelometric Units
• B. NTU
• C. Turbidity Index
• D. Dissolved solids

Answer: (A)

Turbidity is a measure of how cloudy water is, determined by how much light is scattered by suspended particles. This scattering is most accurately captured with a nephelometer, which detects light at a 90-degree angle to the incoming beam. The results from this method are reported as Nephelometric Turbidity Units, reflecting the nephelometric measurement basis. In contexts like this, describing the unit as Nephelometric Units communicates the same idea—the turbidity value comes from a nephelometric measurement—even though NTU is the common abbreviation. The other options don’t fit because dissolved solids describe a different parameter, and a Turbidity Index isn’t a standard unit, while NTU is the precise abbreviation for Nephelometric Turbidity Units.