Fluorobenzene $(C_{6} H_{5} F)$ can be synthesized in the laboratory:
(A) By heating phenol with $H F$ and $K F$
(B) From aniline by diazotization followed by heating the diazonium salt with $H B F_{4}$ .
(C) By direct fluorination of benzene with $F_{2}$ gas
(D) By reacting bromobenzene with $N a F$ solution

Answer

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Hint: As we know that the fluorine atom is very small in size and also is an electron rich atom and

F_{2}

gas is very explosive in nature so if we use fluorine atom in direct substitution it could be very harmful in laboratory.

Complete step by step answer:
If we use fluorine gas directly it can be very explosive due to its very small size and more electrons around the fluorine nucleus.
So in laboratory we synthesis

(C_{6} H_{5} F)

indirectly, which is known as Balz-Schiemann reaction in which we will take aniline as a substrate which will react with

H N O_{2}

(nitrous acid) in the presence of fluoroboric acid and gives a product diazonium salt. As the diazo group is a good leaving group so by reacting diazo-benzene with

H B F_{4}

,this fluoroboric acid attacks the diazo group and replaces diazo with fluorine atom. The

H B F_{4}

gives fluoride ion as a nucleophile which attacks on diazo group. So the final product we will get as

(C_{6} H_{5} F)

.
The mechanism is shown as below.

Therefore, the correct option is option (B).
Note:
Diazotization can also occur in the presence of other acids such as sulphuric acid, hydrochloric acid.