Which of the following pairs of gases are pollutants from car exhaust?

Step 1: Analyze the question We need the pair in which both gases are pollutants released in car exhaust.

Step 2: Concept Car engines burn petrol or diesel in air. Exhaust gases include:

• Carbon(II) oxide (CO): from incomplete combustion; it is toxic.
• Nitrogen(II) oxide (NO): formed when nitrogen and oxygen in air react at the engine's high temperature; it is a pollutant and contributes to acid rain.
• Carbon(IV) oxide (CO₂): a product of complete combustion; it is a greenhouse gas, but in this kind of question it is usually not treated as a poisonous pollutant.
• Sulphur(IV) oxide (SO₂): formed from sulphur impurities in the fuel (more so with diesel).
• Nitrogen (N₂) and oxygen (O₂): normal components of air, not pollutants.

Step 3: Check each option

• A. NO and CO₂: NO is a pollutant, but CO₂ is typically considered a normal combustion product and not a poisonous pollutant. Partly correct only.
• B. CO₂ and N₂: N₂ is harmless. Wrong.
• C. CO and SO₂: both are pollutants. SO₂ comes from sulphur impurities in fuel, and CO from incomplete combustion.
• D. CO and O₂: oxygen is not a pollutant. Wrong.

Step 4: Answer

(Note: option A is a tricky one, because NO is indeed a real car exhaust pollutant, and CO₂ is sometimes counted as one because of global warming. But since the question asks for a pair of pollutants and C has two undisputed ones, C is the best choice.)

Exam tip: Remember the common car exhaust pollutants: CO, NOx, SO₂, unburnt hydrocarbons, and lead compounds (from leaded petrol). Eliminate options containing N₂ or O₂ immediately, since these are harmless components of air.