Which of the following pairs of atomic numbers represents elements belonging to the same group?

Options

A. 11 and 20
B. 12 and 30
C. 13 and 31
D. 14 and 33

Answer

To determine which pairs of atomic numbers represent elements belonging to the same group in the periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Numbers**: We have the following pairs of atomic numbers to analyze: (11, 20), (12, 13), (13, 31), and (14, 33).

2. **Locate Each Atomic Number on the Periodic Table**:
- **Atomic Number 11**: This is Sodium (Na), which is in Group 1.
- **Atomic Number 20**: This is Calcium (Ca), which is in Group 2.
- **Conclusion**: 11 and 20 are not in the same group.

3. **Check the Next Pair (12, 13)**:
- **Atomic Number 12**: This is Magnesium (Mg), which is in Group 2.
- **Atomic Number 13**: This is Aluminum (Al), which is in Group 13.
- **Conclusion**: 12 and 13 are not in the same group.

4. **Check the Pair (13, 31)**:
- **Atomic Number 13**: This is Aluminum (Al), which is in Group 13.
- **Atomic Number 31**: This is Gallium (Ga), which is also in Group 13.
- **Conclusion**: 13 and 31 are in the same group.

5. **Check the Last Pair (14, 33)**:
- **Atomic Number 14**: This is Silicon (Si), which is in Group 14.
- **Atomic Number 33**: This is Arsenic (As), which is in Group 15.
- **Conclusion**: 14 and 33 are not in the same group.

6. **Final Answer**: The only pair of atomic numbers that represents elements belonging to the same group is (13, 31).