Which of the following halide is most reactive towards Nucleophilic substitution reactions ?

Options

A. `C_(2)H_(5)Br`
B. `C_(2)H_(5)Cl`
C. `C_(2)H_(5)F`
D. `C_(2)H_(5)I`

Explanation

To determine which halide is most reactive towards nucleophilic substitution reactions, we need to analyze the bond strengths between carbon and the halogen atoms in the halides.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Substitution**:
- Nucleophilic substitution reactions involve a nucleophile attacking a carbon atom that is bonded to a leaving group (in this case, a halogen).
- The leaving group (halogen) must be able to leave easily for the reaction to proceed.

2. **Bond Strength Consideration**:
- The reactivity of halides in nucleophilic substitution is influenced by the bond strength between the carbon and the halogen (C-X bond).
- Weaker C-X bonds will break more easily, leading to a higher rate of nucleophilic substitution.

3. **Analyzing Halogens**:
- The halogens in order of increasing bond strength with carbon are:
- C-F (Fluorine) - strongest bond
- C-Cl (Chlorine)
- C-Br (Bromine)
- C-I (Iodine) - weakest bond
- As we move down the group in the periodic table, the size of the halogen increases, leading to longer and weaker bonds with carbon.

4. **Determining Reactivity**:
- Since the C-I bond is the weakest among the halides, it will break more easily during nucleophilic substitution.
- Therefore, alkyl iodides (R-I) will be the most reactive towards nucleophilic substitution reactions compared to alkyl fluorides, chlorides, and bromides.

5. **Conclusion**:
- The halide that is most reactive towards nucleophilic substitution reactions is **Iodide (I)**.

### Final Answer:
D. Iodide (I)