Catalytic converters, made of platinum palladium and rhodium, change…

The correct answer is Option (2) → Carbon dioxide and water

Option (1) Carbon monoxide and water — Incorrect. Carbon monoxide is itself a poisonous gas the converter removes, by turning it into CO₂.

Option (2) Carbon dioxide and water — Correct. A catalytic converter has costly metals, platinum–palladium and rhodium, as catalysts. As the exhaust passes through it, unburnt hydrocarbons are converted into carbon dioxide and water, so they are not released as such.

Option (3) Nitric oxide — Incorrect. Nitric oxide is also removed: it is converted into nitrogen gas.

Option (4) Methane — Incorrect. Methane is a hydrocarbon; the converter does not make it.

Note: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Controlling Vehicular Air Pollution: A Case Study of Delhi – “… Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of poisonous gases. As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively. Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.”