Question

Which of the following is the correct decreasing order of bond dissociation enthalpy of halogens ?

• A. \(\text{F}_2 > \text{Cl}_2 > \text{Br}_2 > \text{I}_2\)
• B. \(\text{I}_2 > \text{Br}_2 > \text{Cl}_2 > \text{F}_2\)
• C. \(\text{Cl}_2 > \text{Br}_2 > \text{F}_2 > \text{I}_2\)
• D. \(\text{Br}_2 > \text{I}_2 > \text{F}_2 > \text{Cl}_2\)

Hint:

Fluorine is an exception: its small size causes strong lone pair repulsion that weakens the F-F bond.

Answer 1

The Correct Option is C

Step 1: Data
$\text{Cl}_2$ 242, $\text{Br}_2$ 193, $\text{F}_2$ 158, $\text{I}_2$ 151 kJ/mol.

Step 2: Sort
Arrange in decreasing order: 242 > 193 > 158 > 151.

Step 3: Explain
Bond strength normally falls as size grows. Fluorine breaks this pattern because of the strong repulsion between lone pairs on its tiny atoms.

Step 4: Answer
The order is Cl2, Br2, F2, I2, option (C).

Final Answer:
The order is Cl2 > Br2 > F2 > I2. This is option (C). \[ \boxed{\text{(C) }\text{Cl}_2 > \text{Br}_2 > \text{F}_2 > \text{I}_2} \]