Given are cyclohexanol `(I)`, acetic acid `(II),2,4,6-`trinitrophenol `(III)` and phenol `(IV)`. In these the order of decreasing acidic character will be:

Options

A. `III gt IV gt II gt I`
B. `III gt II gt IV gt I`
C. `II gt III gt I gt IV`
D. `II gt III gt IV gt I`

Explanation

To determine the order of decreasing acidic character among cyclohexanol (I), acetic acid (II), 2,4,6-trinitrophenol (III), and phenol (IV), we need to analyze the structures and acidity of each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Cyclohexanol (I): An aliphatic alcohol with the structure C6H11OH.
- Acetic Acid (II): A carboxylic acid with the structure CH3COOH.
- 2,4,6-Trinitrophenol (III): A phenolic compound with three nitro groups attached to the benzene ring, which significantly increases its acidity.
- Phenol (IV): A simple aromatic compound with the structure C6H5OH.

2. **Understand Acidity**:
- Acidity is determined by the ability of a compound to donate a proton (H+).
- Carboxylic acids are generally more acidic than alcohols and phenols due to the stability of their conjugate bases after deprotonation.

3. **Compare Acidity**:
- **Cyclohexanol (I)**: As an aliphatic alcohol, it has low acidity. Its conjugate base is not stabilized significantly.
- **Acetic Acid (II)**: It is a carboxylic acid and is more acidic than alcohols and phenols. Its conjugate base (acetate ion) is stabilized by resonance.
- **Phenol (IV)**: More acidic than cyclohexanol due to resonance stabilization of its conjugate base (phenoxide ion).
- **2,4,6-Trinitrophenol (III)**: The presence of three nitro groups (strong electron-withdrawing groups) increases the acidity significantly by stabilizing the conjugate base through resonance and inductive effects.

4. **Order of Acidity**:
- **Most Acidic**: 2,4,6-Trinitrophenol (III) - due to strong electron-withdrawing effects from nitro groups.
- **Next**: Acetic Acid (II) - as a carboxylic acid, it is more acidic than phenol and cyclohexanol.
- **Next**: Phenol (IV) - more acidic than cyclohexanol but less than acetic acid.
- **Least Acidic**: Cyclohexanol (I) - the least acidic among the four.

5. **Final Order**:
- The order of decreasing acidic character is:
- 2,4,6-Trinitrophenol (III) > Acetic Acid (II) > Phenol (IV) > Cyclohexanol (I).

### Conclusion:
The correct order of decreasing acidic character is:
**2,4,6-Trinitrophenol (III) > Acetic Acid (II) > Phenol (IV) > Cyclohexanol (I)**.