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

$A.$ Ammonium salts produce haze in the atmosphere.
$B.$ Ozone is produced when atmospheric oxygen reacts with chlorine radicals.
$C.$ Polychlorinated biphenyls act as cleansing solvents.
$D.$ 'Blue baby' syndrome occurs due to the presence of excess nitrate ions in water.
Choose the correct answer from the options given below:

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

What is the volume percentage of nitrogen gas in the atmosphere (in $\%$)?

Which of the following statements about photochemical smog is wrong?

$A$ factory was started near a village. Soon,the villagers began experiencing the presence of undesirable gases in the atmosphere,leading to symptoms like headaches,chest pain,colds,dry throats,and breathing difficulties. The villagers blamed the smoke emitted from the factory chimney for these problems. Describe what might have happened and provide the chemical equations to support your explanation.