The conversion of benzene diazonium chloride to chlorobenzene is an example of the Sandmeyer reaction.

Sandmeyer Reaction:
The Sandmeyer reaction is a chemical reaction used to convert an aromatic diazonium salt to a new functional group. It involves the substitution of the diazonium group with another functional group, typically through the use of a copper(I) salt as a catalyst. The reaction is named after the Swiss chemist Traugott Sandmeyer, who first described it in the late 19th century.

Reaction Mechanism:
The Sandmeyer reaction proceeds through a series of steps:

1. Diazonium ion formation: The benzene diazonium chloride (C6H5N2Cl) reacts with hydrochloric acid (HCl) to form the diazonium ion (C6H5N2+).

2. Copper(I) salt formation: Copper(I) chloride (CuCl) is added as a catalyst to facilitate the reaction.

3. Nitrogen gas evolution: The diazonium ion loses nitrogen gas (N2) to form a carbocation intermediate.

4. Substitution: The carbocation intermediate reacts with a nucleophile (chloride ion, Cl-) to form the desired product, chlorobenzene (C6H5Cl).

Significance of the Sandmeyer Reaction:
The Sandmeyer reaction is an important tool in synthetic organic chemistry as it allows for the introduction of a wide range of functional groups onto aromatic rings. It is particularly useful for the preparation of aryl halides, which are important intermediates in the synthesis of various organic compounds.

Other Reactions:
- Claisen reaction: The Claisen reaction is a reaction between an ester and a strong base to form a β-keto ester.
- Friedel-Crafts reaction: The Friedel-Crafts reaction is a reaction between an aromatic compound and an alkyl halide or acyl halide to form a substituted aromatic compound.
- Wurtz reaction: The Wurtz reaction is a reaction between alkyl halides and metallic sodium to form a higher hydrocarbon.

Therefore, the conversion of benzene diazonium chloride to chlorobenzene is an example of the Sandmeyer reaction (option C).