Question

Which carbon-halogen bond has the lowest bond enthalpy?

• A. C-Br
• B. C-Cl
• C. C-F
• D. C-I

Hint:

For alkyl halides: \[ C-F > C-Cl > C-Br > C-I \] in bond enthalpy.

Answer 1

The Correct Option is D

Concept:
Bond enthalpy is the energy required to break a bond. A stronger bond has higher bond enthalpy. A weaker bond has lower bond enthalpy. In carbon-halogen bonds, bond strength decreases as the size of halogen increases.

Step 1: Compare halogen sizes.
The size order of halogens is: \[ F < Cl < Br < I \] So iodine is the largest among these.

Step 2: Compare bond length.
As halogen size increases, carbon-halogen bond length increases. So: \[ C-F < C-Cl < C-Br < C-I \] The \(C-I\) bond is the longest.

Step 3: Relate bond length and bond strength.
Longer bonds are generally weaker. Therefore, bond strength order is: \[ C-F > C-Cl > C-Br > C-I \] So bond enthalpy is lowest for: \[ C-I \]

Step 4: Check the options.
Option (A) \(C-Br\) is weaker than \(C-Cl\), but not the weakest.
Option (B) \(C-Cl\) is not the weakest.
Option (C) \(C-F\) is strongest due to small bond length.
Option (D) \(C-I\) is weakest and has the lowest bond enthalpy. Hence, the correct answer is: \[ \boxed{(D)\ C-I} \]