Phenol on standing in air develops a red colour due to formation of `:`

Options

A. cyclohexane
B. resorcinol
C. phenoquinon
D. quinol

Explanation

**Step-by-Step Solution:**

1. **Understanding Phenol**:
- Phenol is an aromatic compound with the formula C6H5OH. It is known to undergo various reactions when exposed to air.

2. **Reaction with Oxygen**:
- When phenol is left standing in air, it reacts with oxygen. This reaction leads to the formation of various products, one of which is a compound known as quinone.

3. **Formation of Quinone**:
- Quinone is a cyclic compound that contains two carbonyl groups (C=O) in a six-membered ring. The reaction of phenol with oxygen involves the oxidation of phenol to form this quinone.

4. **Hydrogen Bonding**:
- The phenol can form hydrogen bonds with the oxygen present in the air. This interaction can stabilize the formation of the quinone compound.

5. **Formation of Phenoquinone**:
- The specific compound formed from the reaction of phenol with oxygen is called phenoquinone. This compound is responsible for the red color observed when phenol stands in air.

6. **Conclusion**:
- Therefore, the red color that develops in phenol upon standing in air is due to the formation of phenoquinone.

**Final Answer**: Phenol on standing in air develops a red color due to the formation of phenoquinone.

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