Final answer:
The greatest health risk from radon is lung cancer.
Step-by-step explanation:
The greatest health risk from radon generally comes from lung cancer. Radon is a radioactive gas that is released from the ground and can easily be inhaled into the lungs. Over time, this internal radon exposure can lead to the development of lung cancer. The incidence of lung cancer in smokers exposed to radon is much higher than in non-smokers exposed to radon, since smoking has already produced some lung damage and the radon simply makes the damage worse.