Correct order of basic strength is :

Options

A. `iii gt ii gt iv gt i`
B. `iv gt ii gt iii gt i`
C. `iii gt ii gt i gt iv`
D. `iii gt i gt ii gt iv`

Answer

To determine the correct order of basic strength among the given compounds, we need to analyze the ability of each compound to donate its lone pair of electrons. The basic strength of an amine is influenced by the electron density on the nitrogen atom, which can be affected by the presence of alkyl groups or resonance effects.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- The compounds we are considering are aniline, ethylamine, ammonia (NH3), and dimethylamine.

2. **Analyze Aniline**:
- Aniline (C6H5NH2) has a lone pair of electrons on the nitrogen atom. However, this lone pair is involved in resonance with the aromatic ring (phenyl group). This resonance decreases the availability of the lone pair for donation, making aniline less basic.

3. **Analyze Ethylamine**:
- Ethylamine (C2H5NH2) has an ethyl group attached to the nitrogen. The ethyl group has a +I (inductive) effect, which increases the electron density on the nitrogen atom. This makes the lone pair more available for donation compared to aniline, thus increasing its basic strength.

4. **Analyze Ammonia (NH3)**:
- Ammonia has no alkyl groups attached to the nitrogen. The electron density on nitrogen is neither increased nor decreased by any substituents, making it a moderate base.

5. **Analyze Dimethylamine**:
- Dimethylamine ((CH3)2NH) has two methyl groups attached to the nitrogen. The +I effect of the two methyl groups significantly increases the electron density on the nitrogen, making the lone pair very available for donation. Therefore, dimethylamine is the strongest base among the compounds considered.

6. **Rank the Basic Strength**:
- Based on the analysis:
- Dimethylamine > Ethylamine > Ammonia > Aniline
- Thus, the correct order of basic strength is:
- Dimethylamine > Ethylamine > Ammonia > Aniline

### Conclusion:
The correct order of basic strength is:
- **Dimethylamine > Ethylamine > Ammonia > Aniline**