Water samples with BOD values of 4ppm and 18 ppm,
Question:

Water samples with BOD values of $4 \mathrm{ppm}$ and $18 \mathrm{ppm}$, respectively, are :

1. Clean and Clean

2. Highly polluted and Clean

3. Clean and Highly polluted

4. Highly polluted and Highly polluted

Correct Option: , 2

Solution:

Clean water would have BOD value $<5 \mathrm{ppm}$ whereas highly polluted water could have BOD value $\geq 17$ $\mathrm{ppm}$.