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

Options

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

Answer

To determine which element of Group 13 does not form M(III) iodide, we first need to analyze the oxidation states of the elements in this group. The elements in Group 13 include Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

### Step-by-Step Solution:

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

2. **Understand the Common Oxidation States**:
- The common oxidation states for these elements are +1 and +3.
- The +3 oxidation state is typically the higher oxidation state, while +1 is the lower oxidation state.

3. **Consider the Inert Pair Effect**:
- As we move down the group from Boron to Thallium, the stability of the +1 oxidation state increases due to the inert pair effect.
- The inert pair effect refers to the tendency of the two electrons in the outermost s subshell to remain paired and not participate in bonding, making the +1 state more stable for heavier elements.

4. **Analyze Each Element**:
- **Boron (B)**: Can form B(III) iodide.
- **Aluminium (Al)**: Can form Al(III) iodide.
- **Gallium (Ga)**: Can form Ga(III) iodide.
- **Indium (In)**: Can form In(III) iodide.
- **Thallium (Tl)**: While Tl can form Tl(I) iodide, it does not commonly form Tl(III) iodide due to the inert pair effect making the +1 state more stable.

5. **Conclusion**:
Based on the analysis, Thallium (Tl) is the element in Group 13 that does not form M(III) iodide due to the stability of its +1 oxidation state over the +3 oxidation state.

### Final Answer:
**Thallium (Tl)** does not form M(III) iodide.