The correct answer is Radon.
Radon is a radioactive noble gas that is found in the Earth’s atmosphere. It is produced by the decay of uranium and thorium in rocks and soil. Radon can enter homes and 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. Exposure to radon can increase the risk of lung cancer by up to 20 times. The risk of lung cancer from radon is higher for smokers than for nonsmokers.
There are several ways to reduce radon levels in homes and buildings. One way is to install a radon mitigation system. A radon mitigation system is a device that removes radon from the air. Another way to reduce radon levels is to improve ventilation in homes and buildings.
Argon, neon, and krypton are not radioactive. They are stable elements that do not decay into other elements.