Answer: A.
It is true that both carbon monoxide and radon are colorless and odorless gasses. Radon is the densest gas known and dissolves in water, which becomes clear, odorless and colorless liquid below its boiling point.
Meanwhile, carbon monoxide is also colorless, tasteless and odorless. This is why it is known to be a silent killer for it interferes with the ability of the hemoglobin to carry oxygen that in turns make an individual feel dizzy, nauseous and suffer stomach ache without even noticing it. However, radon can also be deadly for it can cause cancer especially with constant exposure to it.
