Step 1: Understanding the Question:
The question asks for the major product formed when Phenol reacts with a concentrated mixture of nitric acid.
Step 2: Detailed Explanation:
1. Phenol possesses an \( -OH \) group, which is a powerful activating group and an ortho/para director due to resonance.
2. When dilute \( HNO_3 \) is used at low temperatures, a mixture of o-nitrophenol and p-nitrophenol is obtained.
3. However, when concentrated \( HNO_3 \) is used (often in the presence of concentrated \( H_2SO_4 \)), the nitration is vigorous.
4. All available ortho and para positions (2, 4, and 6) are substituted by nitro (\( -NO_2 \)) groups.
5. The resulting molecule is 2,4,6-trinitrophenol, commonly known as Picric Acid.
Step 3: Final Answer:
The reaction of phenol with concentrated \( HNO_3 \) yields Picric Acid.