Air Pollution

At ground level, ozone is an air pollutant that is a major component of smog which is dangerous for both humans and plants. Long-term ozone exposure has also been shown to reduce life expectancy. 

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. 

The major natural causal agent for acid rain is volcanic emissions. Volcanoes emit acid producing gases to create higher than normal amounts of acid rain or any other form of precipitation such as fog and snow to an extent of affecting vegetation cover and health of residents within the surrounding. 

The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles. Electrical power generation using coal is among the greatest contributors to gaseous pollutions that are responsible for acidic rain. The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited.

Photochemical smog is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone.
Hence option A is the correct answer.

Smog is two types:-
1) Classical smog is also called as London smog or sulphurous acid smog.
2) Photochemical smog is also called as Los angles smog.

Smog is two types:
1) Classical smog is also called as London smog or sulphurous acid smog.
2) Photo chemical smog is also called as Los angles smog.

Smog is two types:
1) Classical smog is also called as London smog or sulphurous acid smog.
2) Photochemical smog is also called as Los angles smog. 
Hence option D is correct.

$SO _2$ is a major gaseous pollutant found in the lower atmosphere. They are the compounds of sulphur and oxygen molecules. So when the fuels such as coal and oil are burnt, it leads to emission of $SO _2$ gas. 

$SO _2, O _3, NO _x$ causes pollution. They are examples of smog or photochemical smog. But $H _2$ being a clean fuel does not pollute the air.

Acid rain is the state when pH of rain falls 5.6. It is mainly due to the presence of oxides of sulphur and nitrogen ( $ NO _2 $ and  $ SO _2 $ in the atmosphere. They are transported into the atmosphere by wind an other air currents. 

The main source of pollution in metro cities is automobile exhausts. 

When gases like $NO _2$ and $SO _3$ go into the atmosphere and react with water and form $H _2SO _4$ and $HNO _3$, these acids come along with rain water and hence it is known as acid rain.

The International Agency for Research on Cancer (IARC) part of the World Health Organisation announced that it had reclassified diesel exhaust as a 'definite carcinogen in highest category (Category 1). When diesel burns inside an engine it releases two potentially cancer-causing things: microscopic soot particles, and chemicals called polycyclic aromatic hydrocarbons or PAHs. There are three possible ways these can cause cancer. The microscopic particles making up diesel exhaust particulate matter are less than one-fifth the thickness of a human hair. They are small enough to penetrate deep into the lungs, causing respiratory disease. Inhaled PAHs could directly damage the DNA in the cells of our lungs leading to cancer. Secondly, the soot particles can get lodged deep inside the lungs, causing long-term inflammation, and thirdly this can increase the rate at which cells divide. So if any nearby lung cells pick up random mutations, this inflammation could make them more likely to grow and spread.