Benzene reacts with chlorine in sunlight to give a final product C6H6Cl6.

Explanation:
When benzene (C6H6) reacts with chlorine (Cl2) in the presence of sunlight, it undergoes a substitution reaction known as chlorination. This reaction is an example of an electrophilic aromatic substitution reaction.

Here is the step-by-step mechanism of the reaction:

1. Initiation:
- In the presence of sunlight, chlorine molecules (Cl2) dissociate homolytically to form chlorine radicals (Cl•).

2. Propagation:
- The chlorine radical (Cl•) attacks the benzene molecule (C6H6), forming a sigma complex.
- The sigma complex is an intermediate in which one of the carbon-hydrogen bonds in benzene is replaced by a carbon-chlorine bond.
- The sigma complex is resonance-stabilized, resulting in the delocalization of the positive charge on the carbon atom.

3. Termination:
- The sigma complex undergoes deprotonation, resulting in the formation of a chlorobenzene molecule (C6H5Cl) and a hydrogen chloride molecule (HCl).
- The chlorine radical (Cl•) generated in the previous step can initiate further chlorination reactions by attacking other benzene molecules, leading to the formation of additional chlorobenzene molecules.

Overall, the reaction proceeds through multiple substitution steps until all six hydrogen atoms in benzene are replaced by chlorine atoms. As a result, the final product obtained is hexachlorobenzene (C6H6Cl6).

The correct answer is option B: C6H6Cl6, which represents hexachlorobenzene.