Radon is a radioactive gas formed in the decay of uranium that is a dangerous air pollutant. Radon typically enters a building through cracks in the foundation.
Neutron is an electrically neutral subatomic particle with a mass approximately equal to one atomic mass unit; generally found within an atomic nucleus.
Proton is a term used to describe a subatomic particle with a charge of +1 and a mass of approximately one atomic mass unit; generally found within an atomic nucleus.
Element (chemical) is a term used to describe a substance that cannot be broken down into two or more new substances by chemical or physical processes