The decrasing basic order of the following is:
i. `Me_(2)N - NMe_(2)`, ii. `MeNH-NHMe`
iii. `H_(2)N - NH_(2)`, iv. `NH_(3)`

Options

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

Explanation

To determine the decreasing basic order of the given compounds, we need to analyze the basicity of each compound based on the presence of nitrogen atoms and the influence of substituents like methyl groups.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- i. \( Me_2N - NMe_2 \) (Dimethylhydrazine)
- ii. \( MeNH - NHMe \) (Methylhydrazine)
- iii. \( H_2N - NH_2 \) (Hydrazine)
- iv. \( NH_3 \) (Ammonia)

2. **Understanding Basicity:**
- Basicity refers to the ability of a compound to donate a lone pair of electrons. The more electron-donating groups attached to the nitrogen atoms, the more basic the compound will be.

3. **Count the Nitrogen Atoms:**
- Compounds i, ii, and iii have two nitrogen atoms, while compound iv (NH3) has only one nitrogen atom. This suggests that compounds with two nitrogen atoms will generally be more basic than NH3.

4. **Evaluate Electron-Donating Effects:**
- **Compound i**: \( Me_2N - NMe_2 \) has four methyl groups (two on each nitrogen). Methyl groups are electron-donating, which increases the electron density on the nitrogen atoms, making this compound the most basic.
- **Compound ii**: \( MeNH - NHMe \) has two methyl groups (one on each nitrogen). This still provides some electron-donating effect but less than compound i.
- **Compound iii**: \( H_2N - NH_2 \) has no methyl groups, so it has the least electron-donating effect among the three compounds with two nitrogen atoms.
- **Compound iv**: \( NH_3 \) has no electron-donating groups and only one nitrogen atom, making it the least basic overall.

5. **Rank the Compounds:**
- Based on the analysis, we can rank the compounds in decreasing order of basicity:
1. \( Me_2N - NMe_2 \) (most basic)
2. \( MeNH - NHMe \)
3. \( H_2N - NH_2 \)
4. \( NH_3 \) (least basic)

### Final Basicity Order:
The decreasing basic order of the compounds is:
\[ Me_2N - NMe_2 > MeNH - NHMe > H_2N - NH_2 > NH_3 \]