An epidemiological study links indoor exposure to a naturally occurring radioactive gas that seeps from soil and rock into poorly ventilated homes. After active smoking, this gas is the second leading cause of lung cancer. The gas is:

• A Formaldehyde
• B Thorium dust
• C Carbon monoxide
• D Radon ✓

Explanation

Radon is a colourless, odourless radioactive gas arising from uranium-238 decay in soil and building materials. It accumulates in poorly ventilated basements and ground-floor rooms, and its alpha-emitting daughters irradiate bronchial epithelium, making it the second leading cause of lung cancer after smoking. Formaldehyde is a chemical indoor pollutant linked to nasopharyngeal cancer, not a radioactive gas, and thorium dust is not a household gas hazard.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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