Question

Which of the following is a mutagen?
(A) $S{O_2}$
(B) $C{O_2}$
(C) $CO$
(D) $HN{O_2}$

Answer 1

Mutagen is anything that causes a mutation (a change in the DNA of a cell). DNA changes caused by mutagens may harm cells and cause certain diseases, such as cancer. Examples of mutagens include radioactive substances, X-rays, ultraviolet radiation, and certain chemicals.

Complete answer:
Mutagen is any physical or chemical agent that changes the genetic material usually DNA of an organism and thus increases the frequency of mutations above the natural level. Most of the mutagens are carcinogens.
Physical mutagens include ionizing radiations like X-rays, gamma rays; ultraviolet radiations.
Chemical mutagens include ROS (reactive oxygen species), deaminating agents $HN{O_2}$ , etc.
$S{O_2}$ , $C{O_2}$ and $CO$ is dangerous to health as they can combine with hemoglobin and hinders oxygen transport but they do not cause any change in DNA. Therefore, they are not classified as a mutagen.
In the stomach, Sodium Nitrate is converted to Nitrous Acid ( $HN{O_2}$ ), which acts as a mutagen by deamination (removal of the $N{H_2}$ group) of adenine and/or cytosine to an ether group, thus altering their base pairing.

Hence, the correct answer is option (D).

Note: Nitrous acid ($HN{O_2}$) is a mutagen (a compound that causes mutations). It is thought to operate by changing the structure of some bases in DNA. For example, it is capable of converting adenine to hypoxanthine.
Nitrogen dioxide ( $N{O_2}$ ), Sulphur dioxide ( $S{O_2}$ ), and Carbon monoxide ( $C{O_2}$ ) are important ambient air pollutants.