Answer:
[tex]NaBF_4[/tex]
Explanation:
In this reaction, we must exchange the amino group ([tex]NH_2[/tex]) for a fluorine atom ([tex]F[/tex]). Also, the first step in this reaction is the addition of nitrous acid.
We must remember that the amino group in the presence of nitrous acid produces a diazonium salt. The [tex]N_2[/tex] group is a very good leaving group and many benzene derivatives can be produced from this intermediate (see figure 1).
If what we want is to bond a fluorine atom we must use [tex]NaBF_4[/tex] to be able to produce m-ethylfluorobenzene (see figure 2).
I hope it helps!
