<prompt> Xanthoproteic test is used forReducing sugarsBile saltsAmino acidsKetone bodies  <response>: Xanthoproteic test: The ring systems in phenylalanine, tyrosine and tryptophan undergo nitration on treatment with concentrated nitric acid when heated Salkowski, 1888. The end product is yellow in color which is intensified in strongly alkaline medium. This reaction causes the yellow stain in the skin by nitric acid.Ref: DM Vasudevan, 7th edition, page no: 31 