Why is it necessary to measure the $BOD$ value of water?

Classical smog is a mixture of .....

The stratosphere extends from sea level up to an altitude of $...$ kilometers.

The type of pollution that increases during the daytime and in the presence of $O_{3}$ is

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 .......... .

Give the names of greenhouse gases.