The tendency of forming `M_("aq")^(3+)` is highest for which IIIA group elements ?

Options

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

Answer

To determine which IIIA group element has the highest tendency to form \( M^{3+}_{(aq)} \), we can analyze the elements in this group: boron (B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl).

### Step-by-Step Solution:

1. **Identify the Elements in the Group**:
The IIIA group elements include boron (B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl).

2. **Understand Oxidation States**:
The common oxidation states for these elements are +3 and +1. As we move down the group, the tendency to form +3 oxidation state generally decreases due to the inert pair effect, where the s-electrons are less likely to participate in bonding.

3. **Analyze the Inert Pair Effect**:
- For thallium (Tl), the inert pair effect is significant, leading to a preference for the +1 oxidation state over +3.
- For indium (In) and gallium (Ga), there is also a decrease in the stability of the +3 state as we move down the group.

4. **Examine Boron and Aluminium**:
- Boron (B) typically forms covalent compounds and does not readily form \( B^{3+} \) in aqueous solution.
- Aluminium (Al), on the other hand, has a strong tendency to form \( Al^{3+} \) in aqueous solution due to its favorable ionization energy and smaller ionic radius compared to the heavier elements.

5. **Conclusion**:
Based on the above analysis, aluminium (Al) has the highest tendency to form \( M^{3+}_{(aq)} \) among the IIIA group elements.

### Final Answer:
The element with the highest tendency to form \( M^{3+}_{(aq)} \) is **Aluminium (Al)**.