$SO_2$ pollution is indicated by

The greenhouse gas(es) is/are:
$A$. Carbon dioxide
$B$. Oxygen
$C$. Water vapour
$D$. Methane
Choose the most appropriate answer from the options given below:

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

Given below are two statements:
Statement $I:$ Classical smog occurs in cool humid climate. It is a reducing mixture of smoke,fog and sulphur dioxide.
Statement $II:$ Photochemical smog has components,ozone,nitric oxide,acrolein,formaldehyde,$PAN$ etc.
In the light of above statements,choose the most appropriate answer from the options given below:

Which of the following is not a greenhouse gas?

The main cause of air pollution in large cities is ........