The correct order in aqueous medium of basic strength in case of methyl substituted amines is:

Options

A. ` NH_3 gt Me_3N gt MeNH_2 gt Me_2NH`
B. ` Me_2NH gt Me_3N gt MeNH_2 gt NH_3`
C. `Me_2NH gt MeNH_2 gt Me_3N gt NH_3`
D. ` Me_3N gt Me_2NH gt MeNH_2 gt NH_3`

Answer

To determine the correct order of basic strength of methyl-substituted amines in aqueous medium, we need to analyze the effect of the methyl groups on the nitrogen atom's ability to donate its lone pair of electrons.

### Step-by-Step Solution:

1. **Understanding Basic Strength**: Basic strength of amines is determined by their ability to donate a lone pair of electrons to protons (H⁺). The more readily an amine can donate its lone pair, the stronger the base.

2. **Effect of Methyl Groups**: Methyl groups (–CH₃) are electron-donating groups due to their +I (inductive) effect. The presence of these groups increases the electron density on the nitrogen atom, enhancing its ability to donate electrons.

3. **Types of Amines**: We have the following methyl-substituted amines:
- NH₃ (Ammonia)
- MeNH₂ (Methylamine)
- Me₂NH (Dimethylamine)
- Me₃N (Trimethylamine)

4. **Order of Basic Strength in Aqueous Medium**: In aqueous solutions, steric hindrance and solvation effects also play a significant role. The general trend for basic strength in aqueous medium is:
- 2° amines > 1° amines > 3° amines > NH₃

5. **Analyzing Each Amine**:
- **Dimethylamine (Me₂NH)**: As a 2° amine, it has two methyl groups that increase electron density, making it a strong base.
- **Methylamine (MeNH₂)**: As a 1° amine, it has one methyl group, which also increases electron density but is less than that of dimethylamine.
- **Trimethylamine (Me₃N)**: As a 3° amine, it has three methyl groups, but steric hindrance reduces its basicity compared to 1° and 2° amines.
- **Ammonia (NH₃)**: It has no methyl groups, so it has the lowest basic strength among these amines.

6. **Final Order**: Considering all the effects, the correct order of basic strength in aqueous medium for the given methyl-substituted amines is:
- Me₂NH > MeNH₂ > Me₃N > NH₃

### Conclusion:
The correct order of basic strength in aqueous medium for methyl-substituted amines is:
**Me₂NH > MeNH₂ > Me₃N > NH₃**