The correct option is
C Aluminium
Air pollution refers to any undesirable changes in the physical, chemical or biological characteristics of air due to the addition of substances such as oxides of sulphur, nitrogen, dust, soot, etc. to air. Such substances are known as air pollutants.
Vehicular emissions are major sources of release of air pollutants. Incomplete combustion of fuels such as petrol or diesel results in the formation of pollutants such as unburnt carbon particles, carbon monoxide, aromatic hydrocarbons (naphthalene, anthracene), nitrogen dioxide, sulphur dioxide, etc.
A catalytic converter is a device that converts toxic byproducts into less hazardous substances. They have expensive metals such as platinum, palladium and rhodium as the catalysts for catalyzing a redox reaction (a reaction in which one reactant undergoes oxidation whereas the other gets reduced during the course of reaction). Hence options a, b, and d are incorrect.
The reaction causes unburnt hydrocarbons in the exhausts to get converted into carbon dioxide and water, carbon monoxide to get converted to carbon dioxide and nitric oxide to get converted into nitrogen gas.
Figure : Functions of catalytic converter
Vehicles that are equipped with catalytic converters are required to use unleaded petrol because lead in the petrol causes inactivation of the catalyst.
Platinum, palladium and rhodium are inert metals and have high resistance to oxidation, even at high temperatures. Aluminium is not an inert metal and cannot be used as a catalyst in catalytic converters. Hence option c is correct.
Figure : Catalytic converters