Is a naturally occurring gas that's found in most soils and rocks and can cause lung cancer.
a. radon
b. hydrogen
c. carbon monoxide
d. nitrogen

The answer is Radon. Radon is an odorless, colorless and tasteless gas. It is the heaviest among the noble gases. It is, in fact, radioactive. Radon is considered to be a health hazard. It is so radioactive that further studies become very difficult. When radon decays, radon progeny is produced. These new substances stick to the surfaces of dust particles in air. When inhaled may stick to the lung and airway walls. 

Ibelieve that is false not 100% tho