The decrease in stability of higher oxidation state in p-block with increasing atomic number is due to:

Options

A. Increase in bond energy as going down the group
B. Inert pair effect
C. Both (A) and (B)
D. None is correct

Explanation

To solve the question regarding the decrease in stability of higher oxidation states in p-block elements with increasing atomic number, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding p-block Elements**:
- The p-block elements include groups 13 to 18 of the periodic table. These elements have their outermost electrons in the p orbital.

2. **Oxidation States in Group 13**:
- Group 13 elements (e.g., boron, aluminium, gallium, indium, and thallium) typically exhibit two oxidation states: +1 and +3.
- The +3 oxidation state is generally more stable for lighter elements like boron and aluminium.

3. **Trend Down the Group**:
- As we move down the group from aluminium to thallium, the stability of the +3 oxidation state decreases, while the stability of the +1 oxidation state increases.

4. **Inert Pair Effect**:
- The primary reason for this trend is known as the **inert pair effect**. This effect refers to the tendency of the two s electrons in the valence shell to remain paired and not participate in bonding as we move down the group.
- The inert pair effect becomes more pronounced due to:
- **Poor shielding**: The s electrons are poorly shielded by the d and f electrons present in heavier elements, making them less available for bonding.
- **Increased atomic size**: As the atomic size increases, the energy required to unpair the s electrons is not compensated by the energy released during bond formation.

5. **Conclusion**:
- Therefore, the decrease in stability of the higher oxidation state (+3) with increasing atomic number in p-block elements is primarily due to the inert pair effect.

### Final Answer:
The decrease in stability of higher oxidation states in p-block elements with increasing atomic number is due to the **inert pair effect**.

---