Answer: B. They oxidize hydrocarbons to form less toxic gases.
A catalytic converter is a device which is used in automobile engine to convert the harmful gaseous exhaust into a less toxic pollutant after the process of combustion of the fuel. It conducts an internal redox (oxidation-reduction) reaction in the automobile engine to facilitate such conversion.
On the basis of the above information, They oxidize hydrocarbons to form less toxic gases is the correct option.