NTU stands for which unit?

• A. Natural Turbidity Unit
• B. Formic Turbidity Unit
• C. Nephelometric Turbidity Unit
• D. Nephrology Turbidity Unit

Answer: (C)

Turbidity is read with a nephelometer, which measures how much light is scattered by particles in water. NTU, or Nephelometric Turbidity Unit, is the unit used for that measurement, defined by the turbidity produced by a Formazin standard when read by nephelometry. Among the options, Nephelometric Turbidity Unit is the correct name because it directly reflects the method (nephelometry) and the quantity (turbidity). The other terms aren’t standard or relevant: natural turbidity, formic turbidity, and a term tied to nephrology (kidneys) don’t describe this measurement.