Which of the following is not a representative element ?

Options

A. Z=37
B. Z=31
C. Z=54
D. Z=24

Answer

To determine which of the given elements is not a representative element, we first need to identify the electronic configurations of each element based on their atomic numbers. Representative elements are those found in the s and p blocks of the periodic table, while d block elements are not considered representative.

### Step-by-Step Solution:

1. **Identify the Elements**:
- Option A: Atomic number 37 (Z = 37)
- Option B: Atomic number 31 (Z = 31)
- Option C: Atomic number 54 (Z = 54)
- Option D: Atomic number 24 (Z = 24)

2. **Determine the Electronic Configurations**:
- **For Z = 37 (Rubidium)**:
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
- This configuration indicates that Rubidium is an s-block element.

- **For Z = 31 (Gallium)**:
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹
- This configuration indicates that Gallium is a p-block element.

- **For Z = 54 (Xenon)**:
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
- This configuration indicates that Xenon is also a p-block element.

- **For Z = 24 (Chromium)**:
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵
- This configuration indicates that Chromium is a d-block element.

3. **Classify the Elements**:
- Rubidium (Z = 37): s-block → Representative Element
- Gallium (Z = 31): p-block → Representative Element
- Xenon (Z = 54): p-block → Representative Element
- Chromium (Z = 24): d-block → Not a Representative Element

4. **Conclusion**:
- The element that is not a representative element is **Chromium (Z = 24)**.

### Final Answer:
**Chromium (Z = 24) is not a representative element.**