A colored gas that is known to be poisonous and can readily damage the mucous lining of the lungs is?

Analysis

The question asks us to identify a specific gas based on three characteristics:

1. It is colored.
2. It is poisonous.
3. It specifically damages the mucous lining of the lungs.

Concept Explanation

To solve this, let's look at the properties of the gases listed:

• Hydrogen sulphide ($H_2S$): A colorless gas with a rotten egg smell. It is toxic, but it is not known primarily for its color.
• Carbon(II) oxide ($CO$): A colorless, odorless, and highly poisonous gas. It binds to hemoglobin in the blood, preventing oxygen transport, but it is not a colored gas.
• Chlorine ($Cl_2$): A pale greenish-yellow gas. It is highly reactive and toxic. Because it is a strong oxidizing agent, when inhaled, it reacts with the moisture in the respiratory tract to form hydrochloric acid ($HCl$) and hypochlorous acid ($HOCl$). These acids are highly corrosive and cause severe damage to the mucous membranes of the lungs.
• Sulphur(IV) oxide ($SO_2$): A colorless gas with a pungent, choking smell. While it is an irritant to the lungs, it is not colored.

Step-by-Step Solution

1. Eliminate colorless gases: Options A, B, and D are all colorless gases. This immediately narrows our search down to Option C.
2. Verify the properties of Chlorine: • Color: Chlorine is distinctly greenish-yellow. • Toxicity: It is a well-known poisonous gas used historically in chemical warfare. • Effect on lungs: As explained above, its reaction with water in the lungs creates acidic conditions that destroy the delicate mucous lining, leading to pulmonary edema (fluid in the lungs).

Conclusion

Based on the physical property of being a "colored gas" and the physiological effect on the respiratory system, Chlorine is the correct answer.

Exam Tip: Whenever you see a question about a "greenish-yellow" gas in Chemistry, always think of Chlorine. It is a classic JAMB favorite!