Diagonal relationship is shown by

Options

A. All elements with their diagonally opposite elements.
B. All elements of `3rd` and `4th` periods
C. Some of the elements of `2nd` and `3rd` periods
D. Elements of d-block

Answer

### Step-by-Step Solution:

1. **Understanding Diagonal Relationship**:
- The diagonal relationship in the periodic table refers to the similarity in properties of certain pairs of elements that are diagonally positioned to each other in the periodic table.

2. **Identifying the Relevant Elements**:
- The elements that exhibit this diagonal relationship primarily belong to the 2nd and 3rd periods of the periodic table.
- Notable pairs include:
- Lithium (Li) and Magnesium (Mg)
- Beryllium (Be) and Aluminium (Al)
- Boron (B) and Silicon (Si)

3. **Reason for Diagonal Relationship**:
- The diagonal relationship is mainly due to the similarity in atomic and ionic radii of these elements.
- Elements that are diagonally related often have comparable sizes, which leads to similar chemical properties.

4. **Conclusion**:
- Therefore, the correct answer to the question "Diagonal relationship is shown by" is that it is exhibited by some elements of the 2nd period and some elements of the 3rd period.

### Final Answer:
- The correct option is: **Some elements of the 2nd and 3rd periods.**

---