Which of the following solvents reduces the environmental pollution?

Which of the following does not cause atmospheric pollution?

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

Pure water would have a $BOD$ value of

Which of the following substances combines with hemoglobin in the blood to form carboxyhemoglobin?

The relative contribution of $O_3$,$N_2O$,and $H_2O$ to global warming is in the ratio of ......