Which of the group element does not form M(III) iodide?

Options

A. Al
B. Ga
C. In
D. Tl

Answer

To solve the question "Which of the group elements does not form M(III) iodide?" we will analyze the elements of Group 13 of the periodic table, which includes boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).

### Step-by-Step Solution:

1. **Identify the Group Elements**:
The elements in Group 13 are:
- Boron (B)
- Aluminum (Al)
- Gallium (Ga)
- Indium (In)
- Thallium (Tl)

2. **Determine the Common Oxidation States**:
- Group 13 elements typically exhibit oxidation states of +1 and +3.
- The +3 oxidation state arises from the loss of three valence electrons (one from the s orbital and two from the p orbital).

3. **Analyze the Stability of Oxidation States**:
- As we move down the group from boron to thallium, the stability of the +3 oxidation state decreases, while the stability of the +1 oxidation state increases.
- This trend is influenced by the "inert pair effect," where the s electrons become less available for bonding due to poor shielding by the d and f orbitals.

4. **Examine Each Element**:
- **Boron (B)**: Can form B(III) iodide (BI3).
- **Aluminum (Al)**: Can form Al(III) iodide (AlI3).
- **Gallium (Ga)**: Can form Ga(III) iodide (GaI3).
- **Indium (In)**: Can form In(III) iodide (InI3).
- **Thallium (Tl)**: While thallium can form Tl(I) iodide (TlI), it does not readily form Tl(III) iodide (TlI3) due to the stability of the +1 oxidation state being favored over the +3 state.

5. **Conclusion**:
Based on the analysis, thallium (Tl) is the element that does not form M(III) iodide. Therefore, the answer is:
**Thallium (Tl)** does not form Tl(III) iodide.

### Final Answer:
**Thallium (Tl)**