The correct answer is C. Radon.
Radon is a radioactive gas that is produced by the decay of uranium in rocks and soil. It is the heaviest of the noble gases and is not found in the atmosphere in significant quantities. Radon can enter homes and other buildings through cracks in foundations, walls, and floors. It can also be released from water supplies. Radon is a health hazard because it can cause lung cancer.
Argon, krypton, and xenon are all noble gases that are found in the atmosphere. They are all colorless, odorless, and non-reactive gases. They are used in a variety of applications, including lighting, lasers, and electronics.
Argon is the most abundant noble gas in the atmosphere, making up about 0.93% of the air. It is used in a variety of applications, including lighting, lasers, and electronics.
Krypton is the second most abundant noble gas in the atmosphere, making up about 0.09% of the air. It is used in a variety of applications, including lighting, lasers, and electronics.
Xenon is the third most abundant noble gas in the atmosphere, making up about 0.009% of the air. It is used in a variety of applications, including lighting, lasers, and electronics.