The correct option is (b).
Explanation
Combustion, or burning, is a high-temperature exothermic chemical reaction between a fuel (the reductant) and an oxidant (usually atmospheric oxygen) that produces oxidized products, often in a gaseous mixture termed as smoke.
Statement-wise Analysis:
- Statement 1 is Incorrect. Combustion (burning) strictly requires the presence of a supporter of combustion, which is typically oxygen. Nitrogen is an inert gas under normal conditions and does not support combustion; instead, it acts as a diluent that reduces the rate of combustion. While nitrogen can react at very high temperatures to form oxides, it cannot replace oxygen to sustain the burning of fuel.
- Statement 2 is Correct. Smoke is a collection of airborne particulates and gases emitted when a material undergoes combustion. It consists of unburnt carbon particles (soot), fine dust, and various gases such as carbon dioxide, carbon monoxide, and water vapour.
- Statement 3 is Incorrect. Smoke contains particulate matter (PM 2.5, PM 10) and toxic gases (like carbon monoxide) that are harmful to the respiratory system. Inhalation of smoke can lead to respiratory diseases such as asthma, bronchitis, and lung damage, rather than being beneficial.
Key Takeaway: Burning is an oxidation process requiring oxygen. The resulting smoke is a pollutant mixture of gases and particulate matter that poses significant health risks to the respiratory system.