In which of the following cases `C-C` bond length will be highest?

Options

A. `CH_(3)-CF_(3)`
B. `FCH_(2)-CH_(2)F`
C. `F_(2)CH-CHF_(2)`
D. `CF_(3)-CF_(3)`

Explanation

To determine which `C-C` bond length will be the highest among the given options, we need to analyze the influence of electronegativity and the number of substituents on the carbon atoms. The bond length is influenced by the presence of electronegative atoms, which can pull electron density away from the carbon-carbon bond, thereby affecting its length.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's assume we have four different compounds with varying numbers of fluorine (F) and hydrogen (H) atoms attached to the carbon atoms. For example:
- Compound A: C-C with 3 F on one carbon and 1 H on the other.
- Compound B: C-C with 1 F on one carbon and 2 H on the other.
- Compound C: C-C with 2 F on each carbon.
- Compound D: C-C with 4 F on one carbon and 1 H on the other.

2. **Apply the Bent Rule**:
According to the Bent Rule, more electronegative atoms (like fluorine) will prefer positions that allow them to have more p-character in their hybrid orbitals. This leads to an increase in bond length as the electronegative atom pulls electron density away from the bond.

3. **Analyze Each Compound**:
- **Compound A**: 3 F on one side leads to significant electron withdrawal, decreasing the bond length.
- **Compound B**: 1 F and 2 H will have a moderate effect on bond length; it will be longer than Compound A but shorter than C and D.
- **Compound C**: 2 F on each carbon will also lead to a decrease in bond length due to electron withdrawal.
- **Compound D**: 4 F on one carbon will create a strong electron-withdrawing effect, leading to the greatest decrease in bond length.

4. **Conclusion**:
The bond length will be longest in Compound B (with 1 F and 2 H) because it has the least number of electronegative fluorine atoms affecting the bond compared to the others. The more electronegative atoms present, the shorter the bond length due to increased electron withdrawal.

### Final Answer:
The `C-C` bond length will be highest in Compound B.