Base strength of
(i) `CH_3CH_2^(-)`
(ii) `CH_2=CH^(-)`
(iii) `CH-=C^(-)`

Options

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

Explanation

To determine the base strength of the given anions, we need to analyze their conjugate acids and compare their acidity. The stronger the conjugate acid, the weaker the corresponding base.

### Step-by-Step Solution:

1. **Identify the Bases and Their Conjugate Acids**:
- (i) The base is `CH3CH2^-` (ethyl anion).
- Conjugate acid: Ethane (`CH3CH3`).
- (ii) The base is `CH2=CH^-` (vinyl anion).
- Conjugate acid: Ethylene (`CH2=CH2`).
- (iii) The base is `CH≡C^-` (acetylide anion).
- Conjugate acid: Acetylene (`CH≡CH`).

2. **Determine the Hybridization of Each Conjugate Acid**:
- Ethane (`CH3CH3`): The carbon atoms are sp³ hybridized.
- Ethylene (`CH2=CH2`): The carbon atoms are sp² hybridized.
- Acetylene (`CH≡CH`): The carbon atoms are sp hybridized.

3. **Analyze the s-character of Each Hybridization**:
- sp³ hybridization (Ethane): 25% s-character.
- sp² hybridization (Ethylene): 33% s-character.
- sp hybridization (Acetylene): 50% s-character.

4. **Relate s-character to Acidity**:
- The greater the s-character, the more electronegative the carbon atom becomes, which leads to a stronger C-H bond and thus a more acidic hydrogen.
- Therefore, the order of acidity based on s-character is:
- Acetylene > Ethylene > Ethane.

5. **Determine the Order of Base Strength**:
- Since a stronger conjugate acid corresponds to a weaker base, we can conclude:
- The base strength order is the reverse of the acidity order:
- `CH≡C^-` (acetylide anion) < `CH2=CH^-` (vinyl anion) < `CH3CH2^-` (ethyl anion).

### Conclusion:
The order of base strength is:
**CH≡C^- < CH2=CH^- < CH3CH2^-**