Explanation:
Xanthoprotic test is given by a protein which consists of \(\alpha\)-amino acids containing a benzene ring such as tyrosine, phenyl alanine etc. This yellow colour is due to nitration of benzene ring and this colour is same as that which forms on skin when conc. \(\mathrm{HNO}_{3}\) comes in contact.
\[\begin{array}{*{20}{l}}
{{\text{Protein}} + {\text{Conc}}{\text{.HN}}{{\text{O}}_3} \to } \\
{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\text{Yellow}}\,{\mkern 1mu} {\text{colour}}}
\end{array}\]
