Which of the following correctly shows the order of decreasing basicity -

Options

A. Aniline `gt` o-nitroaniline `gt` p-nitroanilne `gt` m-nitroaniline
B. Anili ne `gt ` p -nitroaniline `gt` o-nitroaniline `gt` m-nitroaniline
C. Aniline `gt` m-nitroaniline `gt ` p- nitroaniline `gt -` o-nitroaniline
D. o-Nitroaniline `gt` p-nitroaniline `gt` aniline `gt` m-nitroaniline

Explanation

To determine the order of decreasing basicity among the given compounds, we will analyze the structures and the effects of substituents on the basicity of each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds we are considering are:
- Aniline (C6H5NH2)
- Meta-nitroaniline (C6H4(NH2)(NO2) at the meta position)
- Para-nitroaniline (C6H4(NH2)(NO2) at the para position)
- Ortho-nitroaniline (C6H4(NH2)(NO2) at the ortho position)

2. **Understand Basicity**: Basicity refers to the ability of a compound to donate a lone pair of electrons. The more available the lone pair is for donation, the more basic the compound is.

3. **Analyze Aniline**:
- Aniline has an amino group (NH2) attached to a benzene ring.
- The lone pair on the nitrogen can participate in resonance with the benzene ring, but it is still relatively available for donation.
- Thus, aniline is moderately basic.

4. **Analyze Meta-nitroaniline**:
- The nitro group (NO2) is an electron-withdrawing group and is positioned at the meta position.
- The inductive effect of the nitro group decreases the electron density on the nitrogen atom, making the lone pair less available for donation.
- Therefore, meta-nitroaniline is less basic than aniline.

5. **Analyze Para-nitroaniline**:
- In para-nitroaniline, the nitro group is also an electron-withdrawing group.
- However, the resonance effect is less significant compared to the ortho position because the lone pair on nitrogen can still participate in resonance, but the nitro group is farther away than in the ortho position.
- Thus, para-nitroaniline is less basic than aniline but more basic than meta-nitroaniline.

6. **Analyze Ortho-nitroaniline**:
- In ortho-nitroaniline, the nitro group is positioned adjacent to the amino group.
- This proximity allows for strong resonance delocalization of the lone pair on nitrogen into the nitro group, significantly reducing the availability of the lone pair for donation.
- Therefore, ortho-nitroaniline is the least basic of the four compounds.

7. **Order of Basicity**: Based on the analysis:
- Aniline > Para-nitroaniline > Meta-nitroaniline > Ortho-nitroaniline

### Final Answer:
The order of decreasing basicity is:
**Aniline > Para-nitroaniline > Meta-nitroaniline > Ortho-nitroaniline**