An element has atomic number 15. What will be the valency/valencies shown by it?

Explanation

The atomic number of the element being 15, it has 15 electrons. The electronic configuration is
`{:(K,L,M),(2,8,5):}` or 2,8,5.
We know that the valency of an element is equal to the number of electrons or 8-number of valence electrons. Hence, the element will have a valency of 5 and 8-5=3. Note. The element is phosphorus which forms `PCl_3` and `PCl_5`