Which of the following statement(s) is`//`are correct regarding anomalous behaviour of first member of group 13-18 elements ?
I. This is due to the absence of d-orbital in valence shell.
II. This is due to the presence of p-orbital in valence shell.
III. This is due to the presence of d-orbital in valence shell.
Choose the correct option.

Options

A. I and II
B. Only II
C. Only I
D. Only III

Answer

To solve the question regarding the anomalous behavior of the first member of group 13 to 18 elements, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Anomalous Behavior**:
- The first members of groups 13 to 18 (Boron, Carbon, Nitrogen, Oxygen, Fluorine, and Neon) exhibit anomalous behavior compared to their subsequent group members. This is primarily due to their electronic configuration and the absence of certain orbitals.

2. **Analyzing Statement I**:
- **Statement I**: "This is due to the absence of d-orbital in valence shell."
- The first members of these groups do not have d-orbitals available in their valence shell. This lack of d-orbitals means they cannot expand their octet, which is a key factor in their anomalous behavior. Therefore, this statement is **correct**.

3. **Analyzing Statement II**:
- **Statement II**: "This is due to the presence of p-orbital in valence shell."
- While the first members do have p-orbitals, the presence of p-orbitals alone does not explain their anomalous behavior. The p-orbitals are present in all members of the group, but it is the absence of d-orbitals that leads to the unique properties of the first members. Hence, this statement is **incorrect**.

4. **Analyzing Statement III**:
- **Statement III**: "This is due to the presence of d-orbital in valence shell."
- This statement is incorrect because the first members of these groups lack d-orbitals in their valence shell. The presence of d-orbitals is actually a characteristic of the heavier elements in these groups. Therefore, this statement is **incorrect**.

5. **Conclusion**:
- Based on the analysis:
- Statement I is correct.
- Statement II is incorrect.
- Statement III is incorrect.
- The correct option is that only Statement I is true.

### Final Answer:
The correct option is **only I**.