Assertion: Alkyl benzene is not prepared in good yield by Friedel-Craft’s alkylation of benzene. Reason: Alkyl halides are less reactive than acyl halides.

By Friedel crafts alkylation, the mixture of mono, di, tri alkylated products is formed which are very hard to separate. So, alkyl benzene is prepared by Friedel craft’s acylation followed by reduction of acyl benzene to alkyl benzene. Alkyl halides are less reactive than acyl halides because in the case of acyl halide the carbonyl carbon is more electrophilic than the carbon atom of alkyl halide. Both assertion and reason are true but it is not a correct explanation. Hence, the correct option is (b).