Question

Which of the following is not a greenhouse gas?
A. $ C\mathop O\nolimits_2 $
B. $\mathop H\nolimits_2 O$
C. $\mathop N\nolimits_2 O$
D. $\mathop O\nolimits_2 $

Answer 1

Hint: Greenhouse gases are gases which absorb infrared radiation emitted by earth’s surface and reradiating it back to Earth’s surface. Also, it is known that diatomic gases do not absorb infrared radiation.

Complete step by step solution:
As we know that $C\mathop O\nolimits_2$ present in normal concentration in air is not a pollutant. Rather it helps to maintain the temperature on earth required for the existence of living organisms.
But due to human activities such as burning of fossil fuels, coal, natural gas, petroleum etc., the amount of air is increasing day by day.
This results in warming of earth’s surface and thus brings about drastic changes in global climate.
Out of the sun's total energy entering into earth’s atmosphere, some radiations are scattered, some are reflected back and the rest is absorbed by the earth.
The radiation or heat absorbed by cannot go to the upper atmosphere and is radiated back to the surface of the earth.
 In this way, additional heat is kept within the lower atmosphere and warming of earth takes place.
This warming of earth is called the “greenhouse effect”. It is similar to the greenhouse used for plants.
And the gases responsible for this warming are known as greenhouse gases. Examples of greenhouse gases: $\mathop H\nolimits_2 O$ vapors, $C\mathop O\nolimits_2$, $C\mathop H\nolimits_4$ , $\mathop O\nolimits_3$, $\mathop N\nolimits_2 O$ etc. Since greenhouse gases absorb infrared radiation but diatomic gases do not absorb infrared radiation undergo vibrational transition and are thus not greenhouse gas.
Therefore, from above we can say that option D is the correct answer.

Note: It should be noted that due to greenhouse effect, there has been drastic climatic change and increase in earth’s average temperature. So, it is important to plant more and more trees in order to reduce the concentration of $C\mathop O\nolimits_2$ in the atmosphere.