Which of the following group 13 elements does not show the inert pair effect?

Options

A. Thallium
B. Gallium
C. Indium
D. Aluminium

Answer

To determine which of the group 13 elements does not show the inert pair effect, we need to analyze the elements in this group and understand what the inert pair effect is.

### Step-by-Step Solution:

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

2. **Understand Inert Pair Effect**: The inert pair effect refers to the tendency of the outermost s-electrons (ns²) to remain non-bonding or inert in heavier elements of a group due to poor shielding by d and f orbitals. This effect becomes more pronounced as we move down the group.

3. **Analyze Each Element**:
- **Boron (B)**: Has the electronic configuration of 1s² 2s² 2p¹. It does not have d or f orbitals, so it does not exhibit the inert pair effect.
- **Aluminum (Al)**: Has the electronic configuration of [Ne] 3s² 3p¹. Similar to boron, it does not have d or f orbitals, so it does not exhibit the inert pair effect.
- **Gallium (Ga)**: Has the electronic configuration of [Ar] 3d¹⁰ 4s² 4p¹. It has d orbitals, and thus it does show the inert pair effect.
- **Indium (In)**: Has the electronic configuration of [Kr] 4d¹⁰ 5s² 5p¹. It also has d orbitals and shows the inert pair effect.
- **Thallium (Tl)**: Has the electronic configuration of [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹. It has both d and f orbitals and shows the inert pair effect.

4. **Conclusion**: Among the group 13 elements, Boron (B) and Aluminum (Al) do not show the inert pair effect. However, since the question asks for one specific element, the most commonly referenced element that does not show this effect is Aluminum (Al).

### Final Answer:
**Aluminum (Al)** does not show the inert pair effect.