a. Catalytic converters are recommended for vehicles, These devices have expensive metals, namely platinum, palladium and rhodium, as the catalysts and are fitted into automobiles for reducing emission of poisonous gases. As the exhaust passes through the catalytic converter, unburnt hydro carbons are converted into carbondioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas.
b. Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.
c. Compressed natural gas is preferred to diesel as a fuel in vehicles because CNG burns most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt. CNG is cheaper than petrol or diesel and cannot be siphoned off by thieves and adulterated like petrol or diesel. The main problem with switching over to CNG is the difficulty of laying down pipelines to deliver CNG through distribution points and ensuring uninterrupted supply.