Arrange the following in the increasing order of ease of nucleophilic substitution reaction
Chlorobenzene (I) 2,4,6 trinitrochlorobenzene (II) 2,4 dinitro- chlorobenzene (III) and 4- nitrochlorobenzene (IV)

Options

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

Answer

To arrange the given compounds in the increasing order of ease of nucleophilic substitution reactions, we need to analyze the influence of the nitro groups on the aromatic ring and their effect on the electron density of the ring.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Chlorobenzene (I)
- 2,4,6-Trinitrochlorobenzene (II)
- 2,4-Dinitrochlorobenzene (III)
- 4-Nitrochlorobenzene (IV)

2. **Understand the Role of Nitro Groups**:
- Nitro groups (–NO2) are strong electron-withdrawing groups. Their presence on the aromatic ring decreases the electron density, making the ring more susceptible to nucleophilic attack.
- The position of the nitro groups (ortho, meta, para) also affects the electron density of the ring.

3. **Analyze Each Compound**:
- **Chlorobenzene (I)**: No electron-withdrawing groups, hence it has the least ease of nucleophilic substitution.
- **4-Nitrochlorobenzene (IV)**: Contains one nitro group at the para position, which will slightly increase the ease of nucleophilic substitution compared to chlorobenzene.
- **2,4-Dinitrochlorobenzene (III)**: Contains two nitro groups at the 2 and 4 positions, significantly increasing the electron deficiency of the ring, thus facilitating nucleophilic substitution.
- **2,4,6-Trinitrochlorobenzene (II)**: Contains three nitro groups at the 2, 4, and 6 positions, making it the most electron-deficient and thus the most reactive towards nucleophilic substitution.

4. **Order of Ease of Nucleophilic Substitution**:
- Based on the analysis, we can arrange the compounds in the increasing order of ease of nucleophilic substitution as follows:
- Chlorobenzene (I) < 4-Nitrochlorobenzene (IV) < 2,4-Dinitrochlorobenzene (III) < 2,4,6-Trinitrochlorobenzene (II)

5. **Final Arrangement**:
- The final order is: **I < IV < III < II**.