Question

Which of the following pollutants is the main product of automobile exhaust?
A. $CO$
B. $C{O_2}$
C. $NO$
D. $Hydrocarbons$

Answer 1

They are produced due to the incomplete combustion of carbon and due to the other metallurgical operations.

Complete step by step solutions:
Photochemical smog is one of the main reasons for air pollutants. It is also known as the summer smog, that is originated when UV light from the sun interacts with the oxides of nitrogen present in the atmosphere. It is mostly seen in highly populated cities that are placed in warm climates. They can be seen as a brown haze.

We know the automobile exhaust and solar energy emits nitrogen oxide and hydrocarbons. After a complex series of chemical reactions involving sunlight, oxides of nitrogen and volatile organic compounds (VOC) the photochemical smog is formed. We can observe that during high traffic, a large amount of nitrogen oxides and volatile hydrocarbons are released. These are mainly due to automobile emissions and industrial discharge.

The photochemical smog formation can be explained as the emission of nitrogen oxide and hydrocarbons from automobiles and solar energy. $N{O_3}$ and ${O_3}$ then react with the unburnt hydrocarbons to form formaldehyde, acrolein and proxy-acyl nitrates (PAN).
The chemical reactions involved are:
$2{C_{(s)}} + {O_2} \to 2C{O_{(g)}}$
These are produced due to the incomplete combustion of carbon. They are mainly released in the air by automobile exhaust.
Photochemical Smog Formation:
$N{O_2}_{(g)} \to N{O_{(g)}} + {O_{(g)}}$
Here we get ${O_{(g)}}$ which is highly reactive since it is very unstable
${O_{(g)}} + {O_2} \rightleftarrows {O_3}_{(g)}$
This unstable oxygen then reacts with the remaining oxygen in the atmosphere to form ozone, ${O_3}$.
This formed ozone is then reacted with $NO$ to form formaldehyde, Acrolein, and PAN
$N{O_{(g)}} + {O_3}_{(g)} \to N{O_2}_{(g)} + {O_2}_{(g)}$
$3C{H_4} + 2{O_3} \to 3C{H_2} = O(formaldehyde) + 3{H_2}O$
$C{H_2} = CHCH = O(Acrolein)$
${C_2}{H_3}N{O_5}(PAN)$
$CO$, $NO$ and $hydrocarbons$ are produced due to the automobile exhaust, among this $CO$ is the main product.

Therefore, option (a) $CO$ is correct

Note:
1. We can say that out of 4 options all 3 are produced during the automobile exhaust, but since the question was about the main product we choose $CO$ as the answer.
2. Also, there are a lot of effects due to this such as ozone depletion. To reduce this we have to eliminate the use of fossil fuels and should start using sustainable energies.