The correct option is A Air pollution
Pollution is the addition of contaminants in the environment which degrades its quality. The air pollution is the major threat which needs to be regulated. A catalytic converter is a device used to reduce the emissions from an internal combustion engine (automobiles and vehicles). Enough oxygen is not available to oxidize the carbon fuel in these engines completely into carbon dioxide and water; thus toxic by-products are produced. Catalytic converters are used in exhaust systems to provide a site for the oxidation and reduction of toxic by-products (like nitrogen oxides, carbon monoxide, and hydrocarbons) of fuel into less hazardous substances, such as carbon dioxide, water vapour, and nitrogen gas.