The number of chlorine atoms in bithionol is

We need to determine the number of chlorine atoms in bithionol. Bithionol is a well-known antiseptic and disinfectant used in medicated soaps. Its IUPAC name is 2,2'-thiobis(4,6-dichlorophenol), and its chemical formula is $$\text{C}_{12}\text{H}_{6}\text{Cl}_{4}\text{O}_{2}\text{S}$$.

We have two phenol rings connected by a sulfur bridge (thio linkage). Each phenol ring carries two chlorine atoms at the 4 and 6 positions. Since there are two such rings, the total number of chlorine atoms is $$2 \times 2 = 4$$.

Hence, the correct answer is $$\boxed{4}$$.