What is the decreasing order of basicity of `1^(@)2^(@)` and `3^(@)` ethy1 amines and ammonia ?

Options

A. `NH_(3) gt C_(2)H_(5)NH_(2) gt (C_(2)H_(5))_(2)NH gt (C_(2)H_(5))_(3)N`
B. `(C_(2)H_(5))_(2)N gt (C_(2)H_(5))_(2)NH gt C_(2)H_(5)NH_(2) gt NH_(3)`
C. `(C_(2)H_(5))_(2)NH gt C_(2)H_(5)NH_(2) gt (C_(2)H_(5))_(3)N gt NH_(3)`
D. `(C_(2)H_(5))_(2)NH gt (C_(2)H_(5))_(3)N gt C_(2)H_(5)NH_(2) gt NH_(3)`

Explanation

To determine the decreasing order of basicity of 1° (one degree), 2° (two degree), and 3° (three degree) ethylamines, as well as ammonia, we need to consider the factors that influence the basicity of these compounds. Basicity in amines is primarily determined by the availability of the lone pair of electrons on the nitrogen atom for donation.

### Step-by-Step Solution:

1. **Understanding Basicity**:
- Basicity refers to the ability of a compound to donate a lone pair of electrons. In the case of amines, the nitrogen atom has a lone pair that can be donated to acids (protons).

2. **Effect of Alkyl Groups**:
- Alkyl groups (like ethyl, C2H5) have a +I (inductive) effect, which means they can donate electron density towards the nitrogen atom. This increases the availability of the lone pair for donation, enhancing basicity.

3. **Steric Hindrance**:
- As the number of alkyl groups attached to the nitrogen increases (from 1° to 3°), steric hindrance also increases. This means that larger groups can hinder the approach of protons to the nitrogen atom, thereby reducing basicity.

4. **Comparing the Amines**:
- **1° Ethylamine (C2H5NH2)**: Has one ethyl group. It has a +I effect, which increases basicity, but there is some steric hindrance.
- **2° Ethylamine ((C2H5)2NH)**: Has two ethyl groups. It has a stronger +I effect compared to 1° amine and less steric hindrance than 3° amine, making it more basic.
- **3° Ethylamine ((C2H5)3N)**: Has three ethyl groups. While it has a strong +I effect, the steric hindrance is significant, which reduces its basicity compared to 2° amine.
- **Ammonia (NH3)**: Has no alkyl groups, so it has no +I effect. Its basicity is lower than that of any of the ethylamines.

5. **Order of Basicity**:
- Based on the above analysis, the order of basicity from highest to lowest is:
- 2° Ethylamine > 3° Ethylamine > 1° Ethylamine > Ammonia

### Final Answer:
The decreasing order of basicity is:
**2° Ethylamine > 3° Ethylamine > 1° Ethylamine > Ammonia**