International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which of the following is a characteristic of nitrogen oxides?

1. They have a sweet smell

2. They are produced in hot car engines

3. They are non-toxic gases

4. They are soluble in fats

The correct answer is: They are produced in hot car engines

Nitrogen oxides are indeed produced in hot car engines as a result of the combustion of fuel. During the high temperatures of an engine, nitrogen and oxygen from the air can react to form various nitrogen oxides, primarily nitrogen monoxide (NO) and nitrogen dioxide (NO2). These compounds are significant pollutants, often contributing to smog and acid rain, and their formation is a key factor in environmental chemistry linked to vehicle emissions. The characteristic of being produced in hot car engines is essential for understanding the broader implications of nitrogen oxides in both environmental science and public health. The production of these gases in automotive engines highlights the impact of transportation on air quality and underscores the importance of regulations aimed at reducing vehicle emissions. Other choices present characteristics that do not accurately describe nitrogen oxides. For instance, nitrogen oxides do not have a sweet smell; in fact, they can have a sharp or acrid odor, which is unpleasant. They are considered toxic gases, particularly nitrogen dioxide, which can cause respiratory issues. Additionally, nitrogen oxides are not soluble in fats; they are primarily soluble in water, which is a critical factor affecting their behavior in the environment and their interactions with other substances.