What is nickel’s electron configuration?

Hint: Electronic configuration of an element tells us about electron distribution in its atomic orbitals. Writing it down follows a standard notation in which all electrons containing orbitals are arranged sequentially with electron number as a superscript.

Complete answer: Nickel (symbolic representation: Ni) is a transition metal which belongs to the d-block of periodic table. Its atomic number is 28 and is located in the fourth period. It is used to make various alloys which are further very useful in making pipes, nails etc. it is also used in rocket engines and gas turbines as it has capability to resist corrosion at drastic conditions.
-While writing down the electronic configuration, certain standardized notation is followed in which we have to first write energy level or shell followed by subshell and its accommodated electrons in superscript. Electronic configuration of Ni is shown below:-
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{8}}4{{s}^{2}}$
-As we can observe that sometimes it takes very long to write the electronic configuration of elements with large atomic numbers. Therefore we can write the abbreviated notation instead of standard notation by replacing the sequence of completely filled atomic orbitals with the noble gas (which has the same electronic configuration as that of the replaced atomic orbitals).
$[Ar]3{{d}^{8}}4{{s}^{2}}$
 Here argon is used for replacing the electronic configuration as [Ar] = $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}$
-Hence, the electronic configuration of Ni = $[Ar]3{{d}^{8}}4{{s}^{2}}$

Note: -Electronic configurations are useful for determining valency of an element as well as its atomic spectra. Elements with similar electronic configuration tend to show similar periodic properties.
-The maximum number of electrons that can be accommodated in a shell = $2{{n}^{2}}$ (where n is the principal quantum number).