Ground-level ozone is formed when which elements react in sunlight?

Ground-level ozone is a significant component of air pollution, commonly forming in the presence of sunlight. The correct response highlights the role of volatile organic compounds (VOCs) in conjunction with other pollutants, such as nitrogen oxides. When VOCs are emitted from sources like vehicles, industrial facilities, and vegetation, they react with nitrogen oxides in the presence of sunlight to create ozone. This process is part of a complex series of reactions that occur during warm, sunny conditions.

By understanding this reaction, it's clear why VOCs and nitrogen oxides are integral in the formation of ground-level ozone. While other components such as carbon monoxide or sulfur dioxide are indeed present in the atmosphere, they do not directly contribute to the formation of ground-level ozone in the same way that the VOCs do with nitrogen oxides. Therefore, the correct answer effectively highlights the chemistry behind ozone formation.