Ncert Exercises & Solutions

Q.40 Is it true that if the dissolved oxygen level drops to zero, the water will
become septic. Give an example which could lower the dissolved oxygen content of an aquatic body.

Ans. Yes, it is true, in case of zero levels of dissolved oxygen (DO), the water becomes septic. Organic pollution like fertilizer in aquatic bodies is responsible for lowering (upto zero) the level of dissolved oxygen.