Rain water is called as acid rain when its $pH$ is below

How can domestic waste be used as manure?

The pollutants which come directly into the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?

Given below are two statements :-
Statement $I :$ The value of the parameter "Biochemical Oxygen Demand $(BOD)$" is important for survival of aquatic life.
Statement $II :$ The optimum value of $BOD$ is $6.5 \ ppm$.
In the light of the above statements,choose the most appropriate answer from the options given below:

Methemoglobinemia ('blue baby' syndrome) disease is associated with

Which of the following is not a greenhouse gas?