How many interhalogen compounds are not possible ?
`IC l,IB r,BrI,ClBr_(3),ClF_(3),BrCl_(5),BrI_(5),ICl_(3),IF_(7)`

Answer

To determine how many interhalogen compounds from the given list are not possible, we will analyze each compound based on the electronegativity of the halogens involved. The halogens in question are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

### Step-by-Step Solution:

1. **Identify the Halogens**: The halogens involved are F, Cl, Br, and I. Their electronegativities decrease in the order: F > Cl > Br > I.

2. **List of Compounds**: The compounds to analyze are:
- ICl
- IBr
- BrI
- ClBr₃
- ClF₃
- BrCl₅
- BrI₅
- ICl₃
- IF₇

3. **Analyze Each Compound**:
- **ICL**: Iodine (I) is less electronegative than chlorine (Cl). Possible.
- **IBR**: Iodine (I) is less electronegative than bromine (Br). Possible.
- **BRI**: Bromine (Br) is more electronegative than iodine (I). Not possible.
- **CLBR₃**: Chlorine (Cl) is more electronegative than bromine (Br). Not possible.
- **CLF₃**: Chlorine (Cl) is less electronegative than fluorine (F). Possible.
- **BRCL₅**: Bromine (Br) is less electronegative than chlorine (Cl). Possible.
- **BRI₅**: Bromine (Br) is more electronegative than iodine (I). Not possible.
- **ICL₃**: Iodine (I) is less electronegative than chlorine (Cl). Possible.
- **IF₇**: Iodine (I) is less electronegative than fluorine (F). Possible.

4. **Count the Possible and Not Possible Compounds**:
- Possible: ICl, IBr, ClF₃, BrCl₅, ICl₃, IF₇ (Total: 6)
- Not Possible: BrI, ClBr₃, BrI₅ (Total: 3)

5. **Conclusion**: Out of the 9 compounds listed, **3 interhalogen compounds are not possible**.

### Final Answer:
**3 interhalogen compounds are not possible.**