Question

Which of the following compounds give a positive neutral FeCl\(_3\) test?

• A. Threonine
• B. Cysteine
• C. Tyrosine
• D. Serine

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The neutral $FeCl_3$ test is a qualitative test used to detect the presence of phenolic groups.
Step 2: Detailed Explanation:
Phenols react with neutral ferric chloride solution to form a violet, green, or blue colored complex.
Looking at the structures of the given amino acids:
- Threonine: Contains an aliphatic alcohol group.
- Cysteine: Contains a thiol (-SH) group.
- Serine: Contains an aliphatic alcohol group.
- Tyrosine: Contains a phenolic group (p-hydroxyphenyl side chain).

Since Tyrosine contains a phenolic group, it will give a positive result for the neutral $FeCl_3$ test.
Step 3: Final Answer:
Tyrosine gives a positive neutral $FeCl_3$ test.