Which of the following components of air is harmful to living beings?

Dust and smoke

The correct answer is option 4. Dust and smoke.

While several components of air can be harmful to living beings under certain conditions, the most accurate and concise answer is Dust and smoke.

Nitrogen and oxygen: These are the two most abundant gases in the atmosphere and are essential for life. While high concentrations of oxygen can be harmful, they're not typically present in everyday situations.

Carbon dioxide and water vapour: While elevated levels of carbon dioxide can be problematic in enclosed spaces due to its impact on respiration, it's not generally considered harmful in typical outdoor conditions. Water vapor, being the main component of humidity, is not inherently harmful.

Smoke and water vapour: While water vapor itself is not harmful, smoke is a mixture of solid and liquid particles suspended in air, often containing harmful chemicals and pollutants. These can irritate the respiratory system, cause coughing and difficulty breathing, and contribute to various health problems, especially in individuals with pre-existing respiratory conditions.

Dust: Similar to smoke, dust particles can also irritate the respiratory system and cause various health issues, especially when inhaled in large quantities or when containing harmful substances like allergens or pollutants.

Therefore, dust and smoke are the most likely components of air to be directly harmful to living beings in everyday situations due to their potential to irritate the respiratory system and potentially contain harmful chemicals.