Question

What is the electron configuration of an element with atomic number $15$ ?

Answer 1

Chemical elements are arranged in the periodic table according to the order of atomic number. The chemical element with atomic number $15$ means the number of electrons and protons present are $15$ . These electrons are written as electronic configuration, which can be written as the number of electrons entered into the orbitals.

Complete answer:
Periodic table is the representation of chemical elements arranged in the vertical columns and horizontal rows. The vertical columns were known as groups and the horizontal rows are known as periods. There are $18$ groups and $7$ periods in the periodic table.
The element with atomic number $15$ means there are $15$ electrons and $15$ protons. These $15$ electrons entered into different orbitals according to the energy of the orbitals. The number of electrons entered into orbitals depends upon the capability of orbitals. S-orbital can accommodate two electrons, p-orbital can accommodate six electrons, d-orbital can accommodate ten electrons, and f-orbital can accommodate fourteen electrons.
The element with atomic number $15$ is phosphorus. The symbol of phosphorus is P.
The $15$ electrons enter into s and p orbitals which can be represented as $1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}$ Thus, the electronic configuration of an element with atomic number $15$ is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}$ .

Note:
The electronic configuration of chemical elements is based on the atomic number. The electrons are entering according to the energy of orbitals. But in some cases, like copper and chromium the electrons enter into other orbitals as they try to attain half or completely filled electronic configuration. Hence, orbital energy must be known while writing the electronic configuration.