Correct Answer: Radon

Solution : The correct answer is Radon

Radon is a noble gas that is employed in cancer therapy. Radon has an atomic number of 86 and is a 6th period element. It is a radioactive noble gas with no aroma or flavour. Radon treatment is a sort of radiation therapy that kills cancer cells by using radon gas. Radon gas is injected into the tumour and decays, emitting alpha particles. Alpha particles are very powerful particles capable of damaging DNA and killing cancer cells.