The question asks for the term that describes the measurement of how suspended materials in water absorb or scatter light.

Turbidity: Defining Water Cloudiness

Turbidity is defined as the measure of the cloudiness or haziness in a fluid, such as water. It is caused by the presence of suspended solids that scatter and absorb light.

Analyzing Water Quality Parameters

Let's look at the options provided:

• Alkalinity: This measures the water's capacity to neutralize acids, related to dissolved carbonates, bicarbonates, and hydroxides. It does not directly measure light scattering.
• Color: While suspended particles can contribute to water color, 'color' itself is not the specific measure of light absorption or scattering by these particles. Color measurement often focuses on dissolved substances or specific wavelengths.
• Hardness: This refers to the concentration of dissolved minerals, primarily calcium and magnesium ions. It is unrelated to the optical properties affected by suspended materials.
• Turbidity: This term specifically quantifies the reduction of light transparency due to suspended particles, directly relating to light absorption and scattering.

Therefore, the measure of absorption or scattering of light by suspended materials in water is correctly identified as turbidity.