The order of decreasing reactivity towards an electrophilic reagent, for the following would be
(a) Benzene (b) Toulene (c ) Chlorobenzene (d) Phenol

Options

A. `dgtbgtagtc`
B. agtbgtcgtd
C. bgtdgtagtc
D. dgtcgtbgta

Answer

To determine the order of decreasing reactivity towards an electrophilic reagent for the compounds: Benzene, Toluene, Chlorobenzene, and Phenol, we need to analyze the electron density in each compound. The higher the electron density, the more reactive the compound is towards electrophiles.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (a) Benzene
- (b) Toluene
- (c) Chlorobenzene
- (d) Phenol

2. **Understand Electrophilic Substitution**:
Electrophilic substitution reactions involve the attack of an electrophile on the electron-rich aromatic ring. The reactivity depends on the electron density of the ring.

3. **Analyze Each Compound**:
- **Benzene**: It has a stable aromatic structure with no substituents that alter its electron density. Thus, it has moderate reactivity.
- **Toluene**: The presence of the methyl group (–CH₃) is an electron-donating group (through +I effect), which increases the electron density on the aromatic ring, making it more reactive than benzene.
- **Chlorobenzene**: The chlorine atom is a deactivating group due to its –I (inductive) effect, which withdraws electron density from the ring. Therefore, it is less reactive than benzene.
- **Phenol**: The hydroxyl group (–OH) is an electron-donating group (through resonance), significantly increasing the electron density on the aromatic ring, especially at the ortho and para positions. This makes phenol the most reactive among the four.

4. **Rank the Reactivity**:
Based on the analysis:
- **Most Reactive**: Phenol (d)
- **Next**: Toluene (b)
- **Then**: Benzene (a)
- **Least Reactive**: Chlorobenzene (c)

5. **Final Order of Reactivity**:
The order of decreasing reactivity towards an electrophilic reagent is:
- (d) Phenol > (b) Toluene > (a) Benzene > (c) Chlorobenzene

### Summary:
The final order of decreasing reactivity towards an electrophilic reagent is:
**Phenol > Toluene > Benzene > Chlorobenzene**