Consider the following reaction,\[X\xrightarrow{{Bromination}}Y\xrightarrow[{ + HCl}]{{NaN{O_2}}}Z\xrightarrow[{{C_2}{H_5}OH}]{{Boiling}}\]Tribromo-benzene. \[X\]is
(A) Benzoic acid
(B) Salicylic acid
(C) Phenol
(D) Aniline

Hint: Organic substance aniline has the chemical formula \[{C_6}{H_5}N{H_2}\]. The simplest aromatic amine is aniline, which consists of an amino group joined to a phenyl group. It is an important commodity chemical for industry and a flexible starting point for the synthesis of fine chemicals. The production of colours, industrial chemicals, and precursors to polyurethane are its principal uses.

Complete Step by Step Solution:
In the question, we have given the reaction \[X\xrightarrow{{Bromination}}Y\xrightarrow[{ + HCl}]{{NaN{O_2}}}Z\xrightarrow[{{C_2}{H_5}OH}]{{Boiling}}\],
In order to know that by using the gas chromatography-mass spectrometry to determine the amount of cyanide in human plasma and urine, tribromo-benzene serves as an internal standard during the derivatization process. And it joins in stoichiometric \[1:2\] molecular complexes with fullerenes.
Let’s notice the process of the conversion of tribromo-aniline to tribromo-benzene:
Let’s start by the bromination of aniline: Aniline is brominated when being in the presence of aqueous \[B{r_2}\].
The reaction is as follow:

(Self made)

Now, let’s consider the second step: Diazotization is carried in the presence of \[NaN{O_2} + HCl\]. The reaction is as follows:

(Self made)

Then, notice the last step which is reduction with \[{C_2}{H_5}OH\]: When the diazonium salt is reduced with \[{C_2}{H_5}OH\]then tribromo-benzene is produced.

(Self made)

Therefore, \[X\]is aniline in the reaction \[X\xrightarrow{{Bromination}}Y\xrightarrow[{ + HCl}]{{NaN{O_2}}}Z\xrightarrow[{{C_2}{H_5}OH}]{{Boiling}}\]Tribromo-benzene.
Thus, the correct option is: (D) Aniline.

Note: It should be noted that the tribromo-benzene is a crucial step in organic synthesis that is mostly used in the creation of pharmaceuticals. The boiling and fusing temperatures of the tribromo-benzene are \[124^\circ C\]and \[271^\circ C\], respectively. It is water insoluble and that can be dissolved in a hot ethanol. In the current preparation, the procedure for producing the tribromo-benzene involves adding ethanol to a reaction flask containing copper sulphate, stirring, and adding vitriol oil. This mixture is then heated in a water bath and treated by adding \[NaNO\]after the raw materials have all dissolved to boiling in batches to finish.