Which of the following shows variation of bond energy (BE) of halogens 

Options

A. `F_2ltCl_2ltBr_2ltI_2`
B. `I_2ltF_2ltBr_2ltCl_2`
C. `Br_2ltCl_2ltI_2ltF_2`
D. `Cl_2ltF_2ltI_2ltBr_2`

Answer

To determine the variation of bond energy (BE) of halogens, we need to analyze the group 17 elements: fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Here’s a step-by-step solution:

### Step 1: Identify the Halogens
The halogens are the elements in group 17 of the periodic table:
- Fluorine (F)
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I)

### Step 2: Understand the Trend in Atomic Size
As we move down the group from fluorine to iodine, the atomic size increases. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons.

### Step 3: Analyze Bond Length
With the increase in atomic size, the bond length also increases. The bond length order for the diatomic molecules of halogens can be summarized as:
- Iodine (I2) > Bromine (Br2) > Chlorine (Cl2) > Fluorine (F2)

### Step 4: Relate Bond Length to Bond Energy
Bond energy is inversely proportional to bond length. This means that as bond length increases, bond energy decreases. Therefore, we would expect the bond energy order to be the opposite of the bond length order.

### Step 5: Expected Bond Energy Order
Based on the bond length, we would initially expect the bond energy order to be:
- F2 > Cl2 > Br2 > I2

### Step 6: Consider the Exception for Fluorine
However, fluorine has a very small atomic size, which leads to significant inter-electronic repulsions between the lone pairs of electrons. This repulsion weakens the bond in F2, making it less stable than expected. As a result, the actual bond energy order is:
- Cl2 > Br2 > F2 > I2

### Step 7: Final Bond Energy Order
Thus, the correct increasing order of bond energy for the halogens is:
- I2 < F2 < Br2 < Cl2

### Conclusion
The variation of bond energy for halogens shows that chlorine has the highest bond energy, followed by bromine, fluorine, and iodine having the lowest bond energy.