The correct answer is Radon.
Radon is a radioactive gas that occurs naturally in the environment. It is produced by the decay of uranium and thorium in rocks and soil. Radon can enter buildings through cracks in foundations, walls, and floors. It can also be released from building materials, such as granite and concrete.
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 highest for smokers and people who live in areas with high levels of radon.
There are several ways to reduce radon levels in homes. One way is to seal cracks and openings in the foundation, walls, and floors. Another way is to install a radon mitigation system. Radon mitigation systems remove radon from the air before it can enter the home.
If you are concerned about radon in your home, you can test the air for radon. Radon testing kits are available at most hardware stores. If you find that your home has high levels of radon, you should take steps to reduce the levels.
Thorium, radium, and plutonium are also radioactive elements, but they are not as common as radon. Thorium and radium are found in rocks and soil, but they are not released into the air in large amounts. Plutonium is a man-made element that is used in nuclear weapons and power plants. It is not found in the environment in large amounts.
Radon is the only radioactive element that is a significant health hazard. It is important to test your home for radon and take steps to reduce the levels if they are high.