Which of the following is a common source of indoor air pollution?

Tobacco smoke is recognized as a common source of indoor air pollution due to the harmful substances it releases into the air. When tobacco is smoked indoors, it emits a variety of pollutants, including tar, nicotine, carbon monoxide, and numerous volatile organic compounds (VOCs). These substances can adversely affect indoor air quality and pose health risks to both smokers and non-smokers through secondhand smoke exposure. This makes tobacco smoke a significant concern for maintaining healthy indoor environments.

The other options, while they may have some impact on indoor air quality, do not typically contribute to indoor air pollution to the same extent. For instance, solar panels do not emit pollutants themselves; rather, they convert sunlight into energy, with minimal environmental impact in indoor settings. Wood flooring can contribute to indoor air quality issues primarily if it is not treated properly or if certain finishes contain harmful chemicals, but its direct contribution to pollution is often less significant than that of tobacco smoke. Exterior wall paint can also release VOCs, especially when first applied; however, its direct source of pollution in indoor air typically diminishes after drying and curing, making it less problematic over time compared to the persistent nature of tobacco smoke exposure in enclosed spaces.