Which free radical is responsible for the depletion of the ozone layer?

Water is considered to be polluted if the dissolved oxygen $(D.O.)$ content is less than $...$ $ppm$ :

Which one of the following statements regarding photochemical smog is not correct?

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

Fill in the blanks:
$(1)$ The types of smog are ..... and ..... .
$(2)$ Ozone in the air reacts with hydrocarbons to form ...... and ...... .
$(3)$ Harmful ultraviolet rays from the sun cause a type of skin cancer known as ...... .
$(4)$ Chlorofluorocarbon compounds are also called .......... .

Given below are two statements:
Statement $I$: An allotrope of oxygen is an important intermediate in the formation of reducing smog.
Statement $II$: Gases such as oxides of nitrogen and sulphur present in the troposphere contribute to the formation of photochemical smog.
In the light of the above statements,choose the correct answer from the options given below: