carbon monoxide (CO) nitrogen oxide (NO) methane (CH_{4}) ozone (O_{3})
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Secondary pollutants are produced in the environment by chemical reactions involving primary or emitted chemicals. Which of the following is a secondary pollutant?
Possibilities:
- carbon monoxide (CO)
- nitrogen oxide (NO)
- methane (CH_{4})
- ozone (O_{3})

ozone (O_{3})