In which of the following element `+1` oxidation state is more stable :

Options

A. B
B. AI
C. Ga
D. Tl

Explanation

To determine which of the following elements has a more stable +1 oxidation state among boron (B), aluminum (Al), gallium (Ga), and thallium (Tl), we can analyze the trend in oxidation states within Group 13 elements.

### Step-by-Step Solution:

1. **Identify the Group 13 Elements**:
The elements in Group 13 of the periodic table are boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).

2. **Understand Oxidation States**:
Group 13 elements can exhibit multiple oxidation states, primarily +3 and +1. The +3 oxidation state is more common in lighter elements like boron and aluminum.

3. **Examine the Trend in Stability**:
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 attributed to the inert pair effect.

4. **Inert Pair Effect**:
The inert pair effect refers to the tendency of the outer s-electrons (in this case, the 6s electrons in thallium) to remain non-bonding or inert, leading to a preference for the +1 oxidation state over the +3 state in heavier elements.

5. **Conclusion**:
Among the given elements, thallium (Tl) shows the most stable +1 oxidation state due to the significant inert pair effect. Therefore, the answer to the question is thallium (Tl).

### Final Answer:
The element in which the +1 oxidation state is more stable is **Thallium (Tl)**.