Which of the following is not a indoor air pollutant?

Which of the following is not a indoor air
pollutant?
a) Carbon monoxide
b) Nitrous oxide
c) Radon
d) Mercury
Correct Answer - D
Ans. is 'd i.e., Mercury
Indoor air pollution refers to chemical. biological and physical
contamination of indoor air, i.e. the pollution of air with in and around
building and structures.
As most of the people work, study, eat, drink and sleep in enclosed
environments (i.e. indoor) where air circulation may be restricted —>
Most people spend large portion of time indoors, as much as 80-
90% of their lives. Therefore, more people suffer from indoor air
pollution than outdoor pollution.