The order of reactivity of :
`phi-CH_(3)` (I), `phi-CH_(2)-CH_(3)` (II), and `phi-C(CH_(3))_(3)` (IV)
Where `phi=C_(6)H_(5)`

Options

A. `IgtIIgtIIIgtIV`
B. `IVgtIIIgtIIgtI`
C. `IIgtIgtIIIgtIV`
D. `IIIgtIIgtIgtIV`

Explanation

To determine the order of reactivity of the given compounds, we need to analyze the structure of each compound and the influence of the alkyl groups on the reactivity of the phenyl ring in electrophilic substitution reactions.

### Step 1: Identify the Compounds
The compounds given are:
1. **I**: `phi-CH₃` (C₆H₅-CH₃)
2. **II**: `phi-CH₂-CH₃` (C₆H₅-CH₂-CH₃)
3. **III**: `phi-C(CH₃)₂` (C₆H₅-C(CH₃)₂)
4. **IV**: `phi-C(CH₃)₃` (C₆H₅-C(CH₃)₃)

### Step 2: Understand the Role of Alkyl Groups
Alkyl groups are electron-donating groups due to hyperconjugation. They increase the electron density on the benzene ring, making it more reactive towards electrophiles. The reactivity is influenced by the number of alpha hydrogens present on the alkyl group.

### Step 3: Count the Alpha Hydrogens
- **Compound I (C₆H₅-CH₃)**:
- The alpha carbon (attached to the benzene) has 3 alpha hydrogens.

- **Compound II (C₆H₅-CH₂-CH₃)**:
- The alpha carbon has 2 alpha hydrogens.

- **Compound III (C₆H₅-C(CH₃)₂)**:
- The alpha carbon has 1 alpha hydrogen.

- **Compound IV (C₆H₅-C(CH₃)₃)**:
- The alpha carbon has 0 alpha hydrogens.

### Step 4: Determine the Reactivity Order
The reactivity of the compounds is directly proportional to the number of alpha hydrogens:
- **Most Reactive**: Compound I (3 alpha hydrogens)
- **Second**: Compound II (2 alpha hydrogens)
- **Third**: Compound III (1 alpha hydrogen)
- **Least Reactive**: Compound IV (0 alpha hydrogens)

### Final Order of Reactivity
The order of reactivity is:
1. **I**: `phi-CH₃` (most reactive)
2. **II**: `phi-CH₂-CH₃`
3. **III**: `phi-C(CH₃)₂`
4. **IV**: `phi-C(CH₃)₃` (least reactive)

### Conclusion
The final order of reactivity is:
**I > II > III > IV**