For which element the inertness of the electron pair will not be observed

Options

A. Sn
B. Fe
C. Pb
D. In

Explanation

To answer the question "For which element the inertness of the electron pair will not be observed?", we need to understand the concept of the inert pair effect and its relation to elements in the p-block of the periodic table.

### Step-by-Step Solution:

1. **Understanding the Inert Pair Effect**:
The inert pair effect refers to the tendency of the outermost s-electrons (the electron pair) to remain non-bonding or inert in heavier elements of groups 13 to 16 of the periodic table. This effect becomes more pronounced as we move down a group.

2. **Identifying the Relevant Elements**:
The inert pair effect is typically observed in heavier elements of the p-block, particularly in groups 13 (like thallium), 14 (like lead), 15 (like bismuth), and 16 (like polonium).

3. **Finding the Exception**:
The inert pair effect is generally absent in lighter elements of these groups. For instance, in group 13, the lighter element boron does not exhibit the inert pair effect.

4. **Conclusion**:
Therefore, the element for which the inertness of the electron pair will not be observed is **Boron (B)**.

### Summary:
- The inert pair effect is absent in lighter elements of the p-block.
- Boron is a prime example where the inert pair effect does not occur.

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