In which of the following compounds , the oxidation number of iodine is fractional ?

Options

A. `IF_(7)`
B. `I_(3)""^(-)`
C. `IF_(5)`
D. `IF_(3)`

Answer

To determine in which of the given compounds the oxidation number of iodine is fractional, we will analyze each compound step by step.

### Step 1: Understand the Concept of Oxidation Number
The oxidation number (or oxidation state) of an element in a compound is a measure of the degree of oxidation of that element. It can be a whole number or a fraction. A fractional oxidation number indicates that the charge is shared among multiple atoms.

### Step 2: Analyze Each Compound

1. **Compound IF7**:
- Iodine (I) is the central atom surrounded by 7 fluorine (F) atoms.
- Each fluorine has an oxidation state of -1.
- Total oxidation state contributed by fluorine = 7 × (-1) = -7.
- To balance this, iodine must have an oxidation state of +7.
- **Oxidation state of I in IF7 = +7 (non-fractional)**.

2. **Compound IF5**:
- Iodine is the central atom surrounded by 5 fluorine atoms.
- Total oxidation state contributed by fluorine = 5 × (-1) = -5.
- To balance this, iodine must have an oxidation state of +5.
- **Oxidation state of I in IF5 = +5 (non-fractional)**.

3. **Compound IF3**:
- Iodine is the central atom surrounded by 3 fluorine atoms.
- Total oxidation state contributed by fluorine = 3 × (-1) = -3.
- To balance this, iodine must have an oxidation state of +3.
- **Oxidation state of I in IF3 = +3 (non-fractional)**.

4. **Compound I3^-** (Iodide ion):
- This compound consists of three iodine atoms sharing a negative charge.
- The total charge is -1, which is shared among the three iodine atoms.
- Therefore, the oxidation state of each iodine atom is -1/3.
- **Oxidation state of I in I3^- = -1/3 (fractional)**.

### Step 3: Conclusion
After analyzing all the compounds, we find that the only compound where the oxidation number of iodine is fractional is **I3^-**.

### Final Answer:
**The oxidation number of iodine is fractional in the compound I3^-**.

---