Which of the following is a secondary pollutant?

Smog

The correct answer is Option (1) - Smog

Smog is a secondary pollutant formed by the interaction of primary pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. It is a mixture of smoke and fog, hence the term "smog." Smog can have harmful effects on human health and the environment, making it a significant concern in urban areas with high levels of air pollution.