The impurities in water which are extremely small size particles and cannot be removed by settling and filtration are known as
- ASuspended impurities
- BColloidal impuritiesCorrect
- CDissolved impurities
- DPicked up impurities
Solution
Concept
Colloidal impurities
Step-by-step solution
1. Particles of size 1 nm to 1 μm stay suspended and pass through filters, so they cannot be removed by plain settling or filtration. 2. They are colloidal impurities and need coagulation.
Explanation
Colloids are very fine particles carrying surface charge, which keeps them from settling.
Why the other options are wrong
Suspended impurities settle or are filtered. Dissolved impurities are ions and molecules. "Picked up impurities" is not a standard class.
Shortcut
Colloids need coagulation.
Common mistake
Choosing dissolved impurities.
Correct answer: B) Colloidal impurities