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The electron configuration for calcium ion:
A. \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}\]
B. \[1{{s}^{2}}2{{s}^{2}}{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}\]
C. \[1{{s}^{2}}2{{s}^{2}}{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{1}}\]
D. \[1{{s}^{2}}\]
E. \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{1}}\]

Last updated date: 18th Jun 2024
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Hint: Electron configuration is the distribution of electrons of an atom, ion or molecule in atomic or molecular orbital. From the periodic table we know calcium exists in the 2nd group and 4th period in s group.

Complete step-by-step answer:
If we know the periodic table then from there we can find that the atomic number of calcium is 20. Atomic number tells us about the number of electrons and protons in an atom.
So, calcium is an s-block 2nd group element and it can give 2 electrons to make 2+ charges on neutral calcium. Calcium ion exists with 2+ charges on it. So, the number of electrons in calcium ions is 18. If we fill these electrons in orbitals from low energy level to high energy level. First, we see the electron configuration of Calcium: \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}\]
So, there are 2 electrons (valence electrons) in the 4s subshell of calcium which is on its highest energy level and it can release these 2 electrons to make itself stable. So, 2+ charges exist on calcium ions. The calcium ions have 18 electrons which are isoelectronic with noble gas argon, and if we fill these electrons in orbital then its electron configuration: \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}\]
So, “A” is the correct answer.

Additional information:
s subshell has one orbital and p subshell has three orbital. The order of electron orbital energy levels, starting from least to greatest, is as follows: 1s, 2s, 2p, 3s, 3p, 4s,3d, 4p, 5s, 4d,5p,6s,4f,5d, 6p, 7s, 5f, 6d, 7p. These energy levels we can find from the “n+l” rule.

Note: The electron configuration of calcium and calcium ion are different. Remember the energy order of subshells and numbers of orbitals they have.