Question

An element has atomic number 15. It will valency of :

• A. 3
• B. 5
• C. 3 and 5
• D. Zero

Answer 1

The correct option is C

3 and 5

The explanation for the correct answer

Option A

The element with the atomic number 15 is Phosphorous ($\mathrm{P}$). It exhibits the valency of 3 and 5.

• The atoms tend to achieve a stable electronic configuration or to have a complete octet in their outermost orbits.
• So, the number of electrons gained, lost, or shared by an atom of an element to complete its octet is known as the valency of the element.
• Some elements show more than one valency, which is called variable valence.
• Phosphorous with atomic number 15 has the electronic configuration 2,8,5.
• So, to complete its octet, one P atom can gain 3 electrons from the other atom. But due to the presence of a vacant d-orbital, they also exhibit the valency of 5.
• Hence Phosphorous can exhibit the 2 valencies (Both 3 and 5).

Conclusion: Hence Option A is correct.