The atomic number of an element is 15. Hence, it will show a valency of

Options

A. 3 only
B. 5 only
C. both 3 and 5
D. neither 3 nor 5

Explanation

To determine the valency of an element with an atomic number of 15, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Element**:
The atomic number of 15 corresponds to the element Phosphorus (P).

2. **Determine the Electronic Configuration**:
The electronic configuration of Phosphorus can be determined by distributing the electrons in the shells. For atomic number 15, the configuration is:
- 2 electrons in the first shell
- 8 electrons in the second shell
- 5 electrons in the third shell
Therefore, the electronic configuration is 2, 8, 5.

3. **Analyze the Outermost Shell**:
The outermost shell (the third shell) has 5 electrons.

4. **Determine Possible Valencies**:
- **Losing Electrons**: If Phosphorus loses 5 electrons, it would achieve a stable electron configuration similar to that of the noble gas preceding it (Neon). This gives it a valency of 5.
- **Gaining Electrons**: Alternatively, if Phosphorus gains 3 electrons, it would also achieve a stable configuration (completing its octet). This gives it a valency of 3.

5. **Conclusion**:
Therefore, the valency of the element can be either 3 or 5.

### Final Answer:
The element with atomic number 15 can show a valency of 3 or 5.

---