The first member of the p-block elements differs from the remaining members of their corresponding groups due to

Options

A. small size and absence of d-orbitals
B. diagonal relationship with other elements
C. difference in ability to form double and triple bonds
D. high ionisation enthalpy.

Answer

To solve the question regarding how the first member of the p-block elements differs from the remaining members of their corresponding groups, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the First Members of the p-Block Elements:**
- The first members of the p-block elements include boron (B), carbon (C), nitrogen (N), oxygen (O), and fluorine (F). Each of these elements is the first in their respective groups.

2. **Understand the Characteristics of the First Members:**
- The first members of the p-block elements are characterized by their small atomic size compared to the other members of their groups. For instance, boron is smaller than aluminum, carbon is smaller than silicon, and so on.

3. **Consider the Role of d-Orbitals:**
- The first members of the p-block elements (B, C, N, O, F) do not have d-orbitals available for bonding, as they are in the second period of the periodic table. In contrast, the subsequent elements in these groups (like Al, Si, P, S, Cl) have d-orbitals available for bonding, which influences their chemical behavior.

4. **Evaluate the Options Given:**
- **Option A:** Small size and absence of d-orbital - This is true for the first members of the p-block.
- **Option B:** Diagonal relationship with other elements - This is not a primary reason for the difference.
- **Option C:** Differ in ability to form double and triple bonds - While this is somewhat true, it is not the primary distinguishing factor.
- **Option D:** High ionization enthalpy - This is also true but is a consequence of the small size rather than a primary distinguishing feature.

5. **Conclusion:**
- Based on the analysis, the correct answer is **Option A: Small size and absence of d-orbital**. This explains why the first members of the p-block elements exhibit different chemical properties compared to the rest of their group.