Which member of group 13 does not exhibit the group valency in its compounds?

Options

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

Answer

To determine which member of group 13 does not exhibit the group valency in its compounds, we can follow these steps:

### Step 1: Identify the Members of Group 13
Group 13, also known as the boron family, includes the following elements:
- Boron (B)
- Aluminium (Al)
- Gallium (Ga)
- Indium (In)
- Thallium (Tl)

### Step 2: Understand the Common Valency of Group 13
The most common valency for the elements in group 13 is +3. This is because these elements have three valence electrons that they can lose to form positive ions.

### Step 3: Analyze the Stability of the +3 Oxidation State
As we move down the group from boron to thallium, the stability of the +3 oxidation state decreases. This is due to the inert pair effect, which refers to the reluctance of the outermost s electrons to participate in bonding.

### Step 4: Explain the Inert Pair Effect
The inert pair effect occurs because the shielding provided by d and f electrons is poor. As a result, the s electrons become less available for bonding. The effect becomes more pronounced as we move down the group.

### Step 5: Determine the Oxidation States of Thallium
In the case of thallium (Tl), which is at the bottom of the group, both d and f orbital electrons are present. The f electrons provide even poorer shielding than d electrons, leading to a greater inert pair effect. Consequently, thallium tends to exhibit a +1 oxidation state more commonly than the +3 state.

### Step 6: Conclusion
Since thallium shows a preference for the +1 oxidation state and does not exhibit the +3 oxidation state as commonly as the other group members, we conclude that thallium is the element in group 13 that does not exhibit the group valency in its compounds.

### Final Answer
The member of group 13 that does not exhibit the group valency in its compounds is **Thallium (Tl)**.

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