Which of the following is a chemical mutagen?

1. Ethyl methane sulphonate and X-rays
2. Sodium azide and UV rays
3. Ethyl methane sulphanate and Sodium azide
4. X-rays, gamma rays and UV rays

The correct option is 3.
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens. Not all mutations are caused by mutagens: so-called "spontaneous mutations" occur due to spontaneous hydrolysis, errors in DNA replication, repair and recombination.