Do most proteins give a positive xanthoproteic test?why?

Question

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Answer 1

A test for the detection of proteins in which concentrated nitric acid reacts with the proteins to form a yellow color that is intensified to orange-yellow by the addition of alkali.

A positive  result stems from the fact that most protein chains contain amino acids which have aromatic rings.  These rings undergo nitration to give derivatives which are yellow.  In basic solution, the yellow color intensifies.

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