The poisonous gas that is released during the combustion of petrol in a car engine 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 .......... .

Which of the following does not cause atmospheric pollution?

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

What are $X$ and $Y$ in the following reaction?
$CF_2Cl_2 \stackrel{UV}{\longrightarrow} X + Y$

Given below are two statements :-
Statement $I :$ The value of the parameter "Biochemical Oxygen Demand $(BOD)$" is important for survival of aquatic life.
Statement $II :$ The optimum value of $BOD$ is $6.5 \ ppm$.
In the light of the above statements,choose the most appropriate answer from the options given below: