Question

Which of the following measures the hardness of water for different salts?

• A. parts per million
• B. parts per trillion
• C. parts per thousand
• D. parts per hundred

Hint:

For most water quality parameters like hardness, salinity, and dissolved solids, \textbf{ppm (parts per million)} or its equivalent \textbf{mg/L (milligrams per litre)} is the standard unit of measurement.

Answer 1

The Correct Option is A

Step 1: Define water hardness. Step 1: Water hardness mainly results from dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. It quantifies the amount of these mineral salts.
Step 2: Recognize common measurement units.
Step 2: Concentrations of dissolved substances in water use practical units for the low levels present. Common water hardness units include:

Milligrams per litre (mg/L).
Parts per million (ppm).
In water, 1 mg/L equals 1 ppm.
Step 3: Assess the choices.
Step 3: "Parts per million" is the standard and most frequently employed unit. "Parts per trillion" is for extremely low concentrations (e.g., trace pollutants), while "parts per thousand" and "hundred" are too large for this context.