Nucleophilic substitution reactions generally expressed as
`Nu^(-) +R-L rarr R-Nu +L^(-)`
Where `Nu^(-) rarr` Nucleophile , `R-L rarr` substrate, `L rarr` leaving group
The best leaving groups are those that become the most stable ions after they depart. since most leaving group leave as a negatibe ion, the best leaving groups are those ions that stabilize a negative charge most effectively. A good leaving group should be
(a) electron-withdrawing to polarize the carbon
(b) stable once it has left (not a strong base)
(c) polaristable to maintain partial bonding with the carbon in the transition state (both `S_(N)1` and `S_(N)2)`. This bonding helps to stabilise the transition state and reduces the activation energy.
Among the following which is feasible?

Options

A. `X^(-) +CH_(3) -CH_(2)-H rarr CH_(3)-CH_(2)-X +H^(-)`
B. `X^(-)+CH_(3)-OH rarr CH_(3)-X +overset(bar(O)H)`
C. `X^(-) +H_(3)C -underset(H)underset(|)overset(o+)(OH)rarr CH_(3)-X +H_(2)O`
D. `X^(-)+CH_(3)-CH_(3)rarr CH_(3)-X +overset(bar(CH_(3)))`

Answer

To determine which nucleophilic substitution reaction is feasible based on the properties of good leaving groups, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Substitution Reactions**:
- Nucleophilic substitution reactions can be represented as:
\[ \text{Nu}^- + \text{R-L} \rightarrow \text{R-Nu} + \text{L}^- \]
- Here, Nu^- is the nucleophile, R-L is the substrate, and L is the leaving group.

2. **Criteria for a Good Leaving Group**:
- A good leaving group should:
- Be electron-withdrawing to polarize the carbon atom.
- Be stable once it has left (should not be a strong base).
- Be polarizable to maintain partial bonding with the carbon in the transition state.

3. **Evaluating Each Reaction**:
- **Option 1**: Leaving group is H^-.
- H^- is not a good leaving group compared to X^-. It is a strong base and does not stabilize the negative charge effectively.
- **Conclusion**: Reaction is **not feasible**.

- **Option 2**: Leaving group is OH^-.
- OH^- is also not a good leaving group compared to X^-. It is a strong base and does not stabilize the negative charge effectively.
- **Conclusion**: Reaction is **not feasible**.

- **Option 3**: Leaving group is H2O.
- H2O is a better leaving group than halides because it can stabilize the negative charge due to its ability to form hydrogen bonds and has two lone pairs on the oxygen atom.
- **Conclusion**: Reaction is **feasible**.

- **Option 4**: Leaving group is CH3^-.
- CH3^- is not a good leaving group compared to X^-. It is a strong base and does not stabilize the negative charge effectively.
- **Conclusion**: Reaction is **not feasible**.

4. **Final Conclusion**:
- The only feasible reaction among the options provided is **Option 3**, where H2O is the leaving group.