Consider the basicity of the following aromatic amines:
(I) aniline
(II) p-nitroaniline
(III) p-methoxyaniline
(IV) p-methylaniline
The correct order of decreasing basicity is:

Options

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

Answer

To determine the correct order of decreasing basicity for the given aromatic amines, we need to analyze the effects of the substituents on the amine group in each compound. Basicity in amines is influenced by the electron-donating or electron-withdrawing effects of the substituents attached to the aromatic ring.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- (I) Aniline: C6H5NH2
- (II) p-Nitroaniline: C6H4(NO2)NH2 (NO2 is a strong electron-withdrawing group)
- (III) p-Methoxyaniline: C6H4(OCH3)NH2 (OCH3 is an electron-donating group)
- (IV) p-Methylaniline: C6H4(CH3)NH2 (CH3 is also an electron-donating group)

2. **Analyze the Effects of Substituents:**
- **Aniline (I)**: The amino group (NH2) is directly attached to the benzene ring, and there are no substituents that affect its basicity. It can easily accept a proton, making it moderately basic.
- **p-Nitroaniline (II)**: The nitro group (NO2) is a strong electron-withdrawing group (-I and -M effect). It destabilizes the positive charge on the conjugate acid formed upon protonation of the amine, making it less basic.
- **p-Methoxyaniline (III)**: The methoxy group (OCH3) is an electron-donating group (+R effect). It stabilizes the positive charge on the conjugate acid, making this compound more basic than aniline.
- **p-Methylaniline (IV)**: The methyl group (CH3) is also an electron-donating group (+I effect). It increases the basicity compared to aniline but is less effective than the methoxy group.

3. **Rank the Basicity:**
- **Most Basic**: p-Methoxyaniline (III) - due to the +R effect from the methoxy group.
- **Next**: p-Methylaniline (IV) - due to the +I effect from the methyl group.
- **Then**: Aniline (I) - moderate basicity with no strong electron-withdrawing or donating effects.
- **Least Basic**: p-Nitroaniline (II) - due to the strong -I and -M effects from the nitro group.

4. **Final Order of Decreasing Basicity:**
- p-Methoxyaniline (III) > p-Methylaniline (IV) > Aniline (I) > p-Nitroaniline (II)

### Conclusion:
The correct order of decreasing basicity is:
**p-Methoxyaniline (III) > p-Methylaniline (IV) > Aniline (I) > p-Nitroaniline (II)**