Fluorobenzene \((C_6H_5F)\) can be synthesized in the laboratory

From aniline by diazotization followed by heating the diazonium salt with \(HBF_4\)

The correct answer is option 2. From aniline by diazotization followed by heating the diazonium salt with \(HBF_4\).

Fluorobenzene can be synthesized in the laboratory by a process called the Balz-Schiemann reaction. In this reaction, aniline is first diazotized to form benzene diazonium chloride. The benzene diazonium chloride is then treated with hydrogen fluoride and boron trifluoride to form fluorobenzene.

The other options are incorrect. Option (1) is incorrect because petrol is a mixture of hydrocarbons and does not contain benzene. Option (3) is incorrect because direct fluorination of benzene with \(F_2\) gas is a very dangerous reaction and is not typically performed in the laboratory. Option (4) is incorrect because reacting bromobenzene with NaF solution will form benzyl fluoride, not fluorobenzene.

 Here is a summary of the steps involved in the Balz-Schiemann reaction:

1. Aniline is diazotized to form benzenediazonium chloride.

2. Benzene diazonium chloride is treated with hydrogen fluoride and boron trifluoride to form fluorobenzene.

The Balz-Schiemann reaction is a relatively safe and easy reaction to perform in the laboratory. It is also a very versatile reaction, as it can be used to synthesize other aryl fluorides as well.