Which of the following is an air pollutant?

Analysis

The question asks us to identify which of the listed substances is considered an air pollutant. An air pollutant is a substance in the atmosphere that has harmful effects on human health, living organisms, or the environment.

Concept Explanation

• O$_2$ (Oxygen): This is a vital component of the atmosphere (about 21%) and is essential for respiration. It is not a pollutant.
• CO (Carbon(II) oxide): This is a colorless, odorless, and highly toxic gas produced by the incomplete combustion of fossil fuels (e.g., in car engines or generators). It binds to hemoglobin in the blood more strongly than oxygen, preventing oxygen transport, which can be fatal. It is a major primary air pollutant.
• H$_2$O$_{(g)}$ (Water vapor): This is a natural component of the atmosphere and part of the water cycle. It is not considered a pollutant.
• O$_3$ (Ozone): While ozone in the stratosphere is beneficial (protecting us from UV radiation), ozone at ground level is a pollutant. However, in the context of standard chemistry examinations, Carbon(II) oxide (CO) is the classic, definitive example of a primary air pollutant resulting from human activity.

Step-by-Step Solution

1. Evaluate O$_2$: Oxygen is necessary for life; therefore, it is not a pollutant.
2. Evaluate CO: Carbon(II) oxide is a byproduct of incomplete combustion. It is toxic to humans and animals because it interferes with the oxygen-carrying capacity of the blood. It is universally classified as a hazardous air pollutant.
3. Evaluate H$_2$O$_{(g)}$: Water vapor is a natural gas and is not harmful to the environment in the context of pollution.
4. Evaluate O$_3$: While ground-level ozone is harmful, CO is the most direct and commonly cited answer for "air pollutant" in JAMB chemistry syllabi due to its immediate toxicity and common source (exhaust fumes).

Comparing these, CO is the most significant and widely recognized air pollutant among the choices provided.

Conclusion

The correct option is B.

Exam Tip

When you see questions about air pollutants in JAMB, look for products of incomplete combustion like CO (Carbon(II) oxide) or oxides of nitrogen (NO$_x$) and sulfur (SO$_x$). These are the "usual suspects" in environmental chemistry questions!