Which one of the following impurities is easiest to remove from waste water?

Suspended solids

Suspended solids in water refer to various impurities like sand, slit, small stones, etc. These are heavy ad get submerged at the bottom of water. They do not easily mix or dissolved easily with water. So, they can be separated from water by various means like sedimentation, water filter, etc.

Bacteria are very minute organisms that are not even visible to naked eyes and thus their removal becomes very difficult. Proper disinfection is required to remove them.

Colloids and other suspended impurities also need special filtration and purification techniques to be separated from the water.