Methemoglobinemia is due to

How many ozone molecules are destroyed by a single chlorine free radical?

Which one of the following gases is reported to retard photosynthesis?

Given below are two statements:
Statement $I$: Chlorofluorocarbons breakdown by radiation in the visible energy region and release chlorine gas in the atmosphere which then reacts with stratospheric ozone.
Statement $II$: Atmospheric ozone reacts with nitric oxide to give nitrogen and oxygen gases,which add to the atmosphere.
For the above statements choose the correct answer from the options given below :

Which layer of the atmosphere is closest to the Earth's surface?

Air pollution that occurs in sunlight is