What is the decreasing order of strength of the bases `OH^(-),NH_(2)^(-),HC-=C^(-) and CH_(3)CH_(2)^(-)`?

Options

A. `CH_(3)CH_(2)^(-) gt NH_(2)^(-) gt HC -=C^(-) gt OH^(-)`
B. `HC -= C^(-) gt CH_(3)CH_(2)^(-) gt NH_(2)^(-) gt OH^(-)`
C. `OH^(-) gt NH_(2)^(-) gt HC -= C^(-) gt CH_(3)CH_(2)^(-)`
D. `NH_(2)^(-) gt HC-=C^(-) gt OH^(-) gt CH_(3)CH_(2)^(-)`

Answer

To determine the decreasing order of strength of the bases \( \text{OH}^-, \text{NH}_2^-, \text{HC} \equiv \text{C}^-, \text{and } \text{CH}_3\text{CH}_2^- \), we need to analyze the basicity of each species based on their structure and the electronegativity of the atoms involved.

### Step-by-Step Solution:

1. **Identify the Species**: We have four species to compare:
- \( \text{OH}^- \) (hydroxide ion)
- \( \text{NH}_2^- \) (amide ion)
- \( \text{HC} \equiv \text{C}^- \) (acetylide ion)
- \( \text{CH}_3\text{CH}_2^- \) (ethyl ion)

2. **Analyze Electronegativity**:
- **Oxygen (in \( \text{OH}^- \))**: Oxygen is highly electronegative, which means it holds onto its lone pairs tightly and is less willing to donate them.
- **Nitrogen (in \( \text{NH}_2^- \))**: Nitrogen is less electronegative than oxygen, making it more willing to donate its lone pair compared to oxygen.
- **Carbon (in \( \text{HC} \equiv \text{C}^- \))**: The carbon in the acetylide ion is sp-hybridized, which gives it a higher electronegativity than sp3 hybridized carbon but lower than nitrogen.
- **Carbon (in \( \text{CH}_3\text{CH}_2^- \))**: The carbon here is sp3 hybridized, which is the least electronegative of the four species.

3. **Determine Basicity**:
- More electronegative atoms hold onto their lone pairs more tightly, making them less basic.
- The order of basicity can be inferred from the electronegativity:
- \( \text{CH}_3\text{CH}_2^- \) (most basic, least electronegative)
- \( \text{NH}_2^- \) (more basic than \( \text{HC} \equiv \text{C}^- \))
- \( \text{HC} \equiv \text{C}^- \) (less basic than \( \text{NH}_2^- \))
- \( \text{OH}^- \) (least basic, most electronegative)

4. **Final Order**: Based on the analysis, the decreasing order of basic strength is:
\[ \text{CH}_3\text{CH}_2^- > \text{NH}_2^- > \text{HC} \equiv \text{C}^- > \text{OH}^- \]

### Conclusion:
The decreasing order of strength of the bases is:
\[ \text{CH}_3\text{CH}_2^- > \text{NH}_2^- > \text{HC} \equiv \text{C}^- > \text{OH}^- \]