Concept:A poisonous gas that is visibly colored and attacks the respiratory tract is chlorine.
Explanation:Chlorine is a yellow-green gas at room temperature.
It has a pungent, irritating smell.
When inhaled, chlorine reacts with moisture in the lungs to form acids that damage the mucous lining.
It can cause coughing, breathing difficulty, and fluid accumulation in the lungs.
The other gases listed are colorless, so they do not fit the description of a colored gas.
Answer:C. chlorine