How turbidity is reported in water quality tests:\r Turbidity values are expressed as what type of measurement?

Introduction / Context:
Turbidity indicates the scattering of light by suspended and colloidal particles in water. It does not directly equal the mass concentration of particles; rather, it is measured optically using standardized devices and scales such as NTU (nephelometric turbidity units) or historical JTU (Jackson Turbidity Units).

Given Data / Assumptions:

• Turbidity is to be reported using standard water quality conventions.
• Options include mass concentration, pH, and color code, which are not turbidity units.
• Recognition that the scale is instrument dependent.

Concept / Approach:
Nephelometric instruments measure light scattered at 90 degrees and report NTU. The Jackson candle turbidimeter historically reported JTU. Both are numeric values tied to instrument calibration standards, not direct mg/L of solids and not pH or color alone.

Step-by-Step Solution:
Match definition: turbidity is an optical property, not a direct gravimetric concentration.Identify correct reporting: numeric units on an arbitrary scale (NTU/JTU).Therefore select the option specifying an instrument scale.

Verification / Alternative check:
Standard Methods for the Examination of Water and Wastewater specify NTU as the standard reporting unit for turbidity with nephelometry, confirming the chosen option.

Why Other Options Are Wrong:

• ppm (mg/L) relates to concentration, not optical scattering magnitude.
• pH measures acidity/alkalinity.
• Color code alone is not a turbidity measurement unit.

Common Pitfalls:

• Assuming a simple conversion exists between NTU and mg/L of solids; particle size, shape, and refractive index affect scattering.
• Using color as a surrogate for turbidity; colored but particle free water can still have low turbidity.

Final Answer:
As numbers on an arbitrary instrument scale (e.g., NTU or JTU)