Arrange the following anilies in decreasing order of basicity
1. `C_(6)H_(5)NH_(2)`
`o-CH_(3C_(6)H_(4)NH_(2)`
3. `m-CH_(3)C_(6)H_(4)NH_(2)`
4. `p-CH_(3)C_(6)H_(4)NH_(2)`

Options

A. `4 gt 1 gt 2 gt 3`
B. `2 gt 4 gt 3 gt 1`
C. `1 gt 2 gt 3 gt 4`
D. `4 gt 3 gt 2 gt 1`

Answer

To arrange the given anilines in decreasing order of basicity, we need to analyze the effects of the substituents on the amino group (-NH2) in each case. The basicity of aniline and its derivatives is influenced by the electron-donating or electron-withdrawing effects of the substituents attached to the benzene ring.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- 1. Aniline: \( C_6H_5NH_2 \)
- 2. Ortho-methyl aniline: \( o-CH_3C_6H_4NH_2 \)
- 3. Meta-methyl aniline: \( m-CH_3C_6H_4NH_2 \)
- 4. Para-methyl aniline: \( p-CH_3C_6H_4NH_2 \)

2. **Analyze Aniline (1)**:
- Aniline has a lone pair on nitrogen that can participate in resonance with the benzene ring, which decreases its basicity. The lone pair is delocalized, making it less available for protonation.

3. **Analyze Ortho-methyl Aniline (2)**:
- The methyl group at the ortho position has a +I (inductive) effect, which increases the electron density on the nitrogen. This enhances the availability of the lone pair on nitrogen, making it more basic than aniline.

4. **Analyze Meta-methyl Aniline (3)**:
- In the meta position, the methyl group has a lesser effect on the nitrogen's lone pair compared to the ortho position. The resonance effect is not as effective here, and while the +I effect is present, it does not significantly increase basicity. Thus, it is less basic than ortho-methyl aniline but more basic than aniline.

5. **Analyze Para-methyl Aniline (4)**:
- The para methyl group also exerts a +I effect, which increases the electron density on nitrogen. However, the resonance effect is not as strong as in the ortho position since the lone pair is still somewhat delocalized. Therefore, it is more basic than aniline but less than ortho-methyl aniline.

6. **Rank the Basicity**:
- Based on the analysis:
- **Ortho-methyl aniline (2)** has the highest basicity due to the strong +I effect.
- **Para-methyl aniline (4)** comes next as it still has a +I effect but is less effective than the ortho position.
- **Meta-methyl aniline (3)** is next, as it has a weaker effect on the nitrogen's lone pair.
- **Aniline (1)** has the lowest basicity due to resonance delocalization of the lone pair.

### Final Order of Basicity:
\[ o-CH_3C_6H_4NH_2 > p-CH_3C_6H_4NH_2 > m-CH_3C_6H_4NH_2 > C_6H_5NH_2 \]

### Conclusion:
The decreasing order of basicity is:
1. \( o-CH_3C_6H_4NH_2 \) (Ortho-methyl aniline)
2. \( p-CH_3C_6H_4NH_2 \) (Para-methyl aniline)
3. \( m-CH_3C_6H_4NH_2 \) (Meta-methyl aniline)
4. \( C_6H_5NH_2 \) (Aniline)