Water Quality Parameters MCQ with answer and solution

Concept

Threshold Odour Number (TON) and Flavour Threshold Number (FTN) show how much dilution is needed before odour or taste can no longer be detected. For public supply, the limit is 3.

Formula

TON = (A + B) / A, where A = volume of sample (ml) and B = volume of odour-free dilution water (ml)

Step-by-step solution

1. TON tells how many times the sample must be diluted with odour-free water until the odour is just not detected. 2. FTN is defined the same way, but for taste or flavour. 3. Standard textbooks (based on CPHEEO practice) say TON and FTN for public drinking water should not exceed 3. 4. So the answer is 3, which is option A.

Explanation

TON and FTN measure the odour and taste of water by dilution. A higher number means a stronger odour or taste. For good drinking water, the value should not be more than 3.

Why the other options are wrong

B, C and D (4, 5 and 6) are higher than the accepted limit of 3 for drinking water.

Shortcut

Odour/taste threshold number for drinking water: maximum 3.

Common mistake

Students confuse TON with the colour limit (5 on the platinum-cobalt scale) and choose 5.