Methane in polluted air reacts with ozone to form which of the following compounds?

Which of the following is responsible for the greenhouse effect?

Which of the following is not an air pollutant?

Given below are two statements :
Statement $I$ : If $BOD$ is $4\,ppm$ and dissolved oxygen is $8\,ppm$,then it is a good quality water.
Statement $II$ : If the concentration of zinc and nitrate salts are $5\,ppm$ each,then it can be a good quality water.
In the light of the above statements,choose the most appropriate answer from the options given below :

$A$ water sample is reported to be highly polluted if the $BOD$ (Biological Oxygen Demand) value of the sample becomes:

Which of the following is a major air pollutant?