Among the halogens, fluorine differs considerably form the other members. The hydrides of halogens also differ in their properties.
Which of the following halogens do not form polyhalide ?

Options

A. F
B. CI
C. Br
D. I

Explanation

To solve the question regarding which halogen does not form polyhalides, we can follow these steps:

### Step 1: Understand the Halogens
The halogens are a group of elements in Group 17 of the periodic table, which includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Each of these elements has unique properties.

**Hint:** Remember that the halogens have different electronic configurations and oxidation states.

### Step 2: Identify the Unique Properties of Fluorine
Fluorine is unique among the halogens due to its high electronegativity and the absence of vacant d-orbitals. Its electronic configuration is 1s² 2s² 2p⁵, which means it does not have any d-orbitals available for bonding.

**Hint:** Consider how the absence of d-orbitals affects the bonding capabilities of fluorine compared to other halogens.

### Step 3: Understand Polyhalides
Polyhalides are species formed when halogens bond with each other, leading to compounds that contain multiple halogen atoms. For example, compounds like CsBr₅, PCl₅, and I₃⁻ are examples of polyhalides. These compounds typically require the presence of vacant d-orbitals to accommodate additional halogen atoms.

**Hint:** Think about the types of compounds that can be formed based on the oxidation states and available orbitals of the halogens.

### Step 4: Analyze the Other Halogens
Other halogens like chlorine, bromine, and iodine have vacant d-orbitals and can exhibit multiple oxidation states (like +1, +3, +5, and +7). This allows them to form various polyhalides.

**Hint:** Compare the oxidation states of fluorine with those of the other halogens to see why they can form more complex compounds.

### Step 5: Conclusion
Since fluorine does not have vacant d-orbitals and can only exhibit a -1 oxidation state, it cannot form polyhalides. Therefore, the halogen that does not form polyhalides is **fluorine (F)**.

**Final Answer:** Fluorine (F) does not form polyhalides.