$\begin{array}{1 1} \text{a. Oxides of sulphur, nitrogen and carbon are the most wide spread air pollutant.} \\ \text{b. pH of drinking water should be between 5.5-9.5} \\ \text{c. Concentration of DO below 6ppm is good for growth of fish.} \\ \text{d. Clean water would have BOD value of less than 5ppm} \end{array}$
