Answer :
Step-by-step explanation:
Atomic number of calcium is 20.
Electronic configuration of calcium is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
Since (1s² 2s² 2p⁶ 3s² 3p⁶) is electronic configuration of a noble gas , Argon.
Therefore, electronic configuration of calcium can also be written as [Ar] 4s².
Electronic configuration can be defined as the distribution of electrons of an atom or molecules in atomic orbitals.
Or
It is the arrangement of the electrons in orbitals around the nucleus.
For example :-
Electronic configuration of some elements :
1. Hydrogen (Atomic no. = 1) = 1s²
2. Helium (Atomic no. = 2) = 1s²
3. Lithium (Atomic no. = 3) = 1s² 2s¹
4. Beryllium (Atomic no. = 4) = 1s² 2s²
5. Baron (Atomic no. = 5) 1s² 2s² 2p¹