Question 101

Ozone is beneficial in the upper atmosphere but harmful near ground level.

Ozone plays a crucial role in protecting life on Earth by absorbing most of the sun's harmful ultraviolet (UV) radiation in the stratosphere. However, at ground level, ozone becomes a pollutant that can cause significant respiratory problems in humans.

A) Carbon monoxide

Carbon monoxide is not beneficial in the upper atmosphere for blocking UV radiation; instead, it is a harmful gas resulting from incomplete combustion of fossil fuels. It poses serious health risks, including impaired oxygen transport in the blood, but does not have the protective qualities associated with ozone.

B) Nitrogen

Nitrogen is a major component of the atmosphere but does not block UV radiation. While it is not harmful at ground level and makes up about 78% of the Earth's atmosphere, it does not serve a protective function against UV rays and thus does not meet the criteria specified in the question.

C) Ozone

Ozone is beneficial in the upper atmosphere because it effectively absorbs UV radiation, protecting living organisms from its harmful effects. Conversely, at ground level, ozone is a major component of smog and can lead to respiratory issues, making it harmful to human health.

D) Radon

Radon is a naturally occurring radioactive gas that can accumulate in buildings, particularly in basements. It is not involved in blocking UV radiation and is primarily a health hazard due to its radioactive properties, which can increase the risk of lung cancer, rather than serving any beneficial role in the atmosphere.

Conclusion

Ozone is uniquely positioned as a gas that provides essential protection against UV radiation in the upper atmosphere while posing health risks at ground level. In contrast, the other options either lack the ability to block UV radiation or are harmful without providing any atmospheric benefits. Thus, ozone is the only correct answer for the described dual role in atmospheric chemistry.