Which of the following oxides of nitrogen is a coloured gas?

• A. N₂O
• B. NO
• C. N₂O₄
• D. NO₂

The oxide of nitrogen that is a colored gas is NO₂ (D). This gas has a distinctive brown color and is known for its role in air pollution and the formation of smog.

Overview of Nitrogen Oxides

Nitrogen oxides (NOx) are a group of gases that include various compounds of nitrogen and oxygen. Here’s a brief look at the options:

• N₂O (Nitrous oxide): A colorless gas, often used as an anesthetic and in agriculture.
• NO (Nitric oxide): Also colorless, it plays a role in various biological processes.
• N₂O₄ (Dinitrogen tetroxide): Colorless at low temperatures but can appear yellowish at higher temperatures.
• NO₂ (Nitrogen dioxide): A reddish-brown gas that is a significant air pollutant.

Importance of NO₂

NO₂ is not only notable for its color but also for its impact on health and the environment. It can irritate the respiratory system and contribute to the formation of ground-level ozone.