The compound X in the reaction, (a) (b) (c) (d)

Friedel craft’s reactions are generally used to attach substituents to the aromatic ring. Friedel craft’s reaction are of two types i.e. alkylation and acylation. The Friedel craft’s alkylation involves the addition of alkyl group to aromatic ring and Friedel craft’s acylation include the addition of acyl group to aromatic ring in the presence of strong Lewis acid catalyst. Hence, the correct option is (b).