Which of the following gives a positive reaction with Ferrous chloride?

PhenylketonuriaDeficiency of phenylalanine hydroxylase is the cause for this disease. The genetic mutation may be such that either the enzyme is not synthesized, or a non-functional enzyme is synthesized.Laboratory Diagnosis A.Blood phenylalanine: Normal level is 1 mg/dl. In PKU, the level is >20 mg/dl. This may be demonstrated by chromatography. Tandem mass spectroscopy is the most reliable test, but is costly.B. Guthrie test is a rapid screening test.C.Ferric chloride test: Urine of the patient contains phenyl ketones about 500-3000 mg/day. This could be detected by adding a drop of ferric chloride to the urine. A transient blue-green color is a positive test. But this is a less reliable test.D.DNA probes are now available to diagnose the defects in phenylalanine hydroxylase and dihydrobiopterin deficiencyRef: Textbook of biochemistry (DM Vasudevan), 6th edition, page no: 207