Only iodine forms hepta-fluroide `IF_(7)`, but chlorine and bromine give penta-flurorides. The reason for this is:

Options

A. Low electron affinity of lodine
B. Unusual pentagonal bipyramidal strucure of `lF_(7)`
C. The the larger lodine atom can accommodate more number of smaller Fluorine atom around it
D. Low chemical reactivity of `lF_(7)`

Answer

To understand why only iodine forms heptafluoride (IF7) while chlorine and bromine only form penta-fluorides (ClF5 and BrF5), we can analyze the electronic configurations and atomic sizes of these halogens.

### Step-by-Step Solution:

1. **Identify the Halogens and Their Electronic Configurations:**
- Fluorine (F): 1s² 2s² 2p⁵ (outer configuration: 2s² 2p⁵)
- Chlorine (Cl): [Ne] 3s² 3p⁵ (outer configuration: 3s² 3p⁵)
- Bromine (Br): [Ar] 4s² 4p⁵ (outer configuration: 4s² 4p⁵)
- Iodine (I): [Kr] 5s² 5p⁵ (outer configuration: 5s² 5p⁵)

2. **Analyze the Atomic Size:**
- Iodine is larger in size compared to chlorine and bromine due to its position in the periodic table. As we move down the group, the atomic size increases because of the addition of electron shells.

3. **Consider the Coordination Number:**
- The larger atomic size of iodine allows it to accommodate more fluorine atoms around it. Specifically, iodine can form bonds with seven fluorine atoms, resulting in the heptafluoride IF7.
- Chlorine and bromine, being smaller, can only accommodate five fluorine atoms, leading to the formation of ClF5 and BrF5.

4. **Conclusion:**
- The ability of iodine to form IF7 while chlorine and bromine form only pentafluorides is primarily due to the larger atomic size of iodine, which allows it to accommodate more fluorine atoms in its valence shell.

### Final Answer:
Only iodine forms heptafluoride (IF7) because its larger atomic size allows it to accommodate seven fluorine atoms, while chlorine and bromine, being smaller, can only form penta-fluorides (ClF5 and BrF5).

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