Question

Nephelometer is used to measure :

• A. Dissolved oxygen
• B. Carbon dioxide
• C. pH
• D. Turbidity

Hint:

Remember: Nephelometry is based on light scattering at a \(90^{\circ}\) angle by suspended particles, making it the standard method for measuring water Turbidity (expressed in NTUs).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Water quality parameters, such as clarity and suspended particulate matter, directly affect primary productivity and fish health in aquatic systems.
The measurement of light-scattering properties of a fluid is used to quantify the concentration of suspended solids.

Step 2: Detailed Explanation:
A nephelometer is an analytical instrument designed to measure the intensity of light scattered by suspended particulates (such as clay, silt, organic matter, and plankton) in a liquid sample.
The measurement technique, known as nephelometry, is typically performed by passing a light beam through the water sample and measuring the scattered light at an angle of \(90^{\circ}\) relative to the incident light path.
This scattered light intensity is directly proportional to the concentration of suspended particles, which represents the turbidity of the water.
Turbidity is expressed in Nephelometric Turbidity Units (NTU).
Let us review the measurement devices for the other parameters:
1. Dissolved oxygen: Quantified using a polarographic or optical DO probe or chemically via the Winkler titration method.
2. Carbon dioxide: Measured by titrating the water sample with a standard alkaline solution (like Sodium Hydroxide) using phenolphthalein indicator.
3. pH: Measured electronically using a glass electrode pH meter or colorimetrically with pH indicator strips.

Step 4: Final Answer:
Therefore, a nephelometer is used to measure Turbidity.