Final answer:
Calcium's ground-state electron configuration is [Ar]4s², as calcium is located in the s block of the periodic table and has two valence electrons in the 4s orbital.
Step-by-step explanation:
The ground-state electron configuration of a calcium atom can be determined based on its position on the periodic table. Calcium (Ca), with atomic number 20, is located in the second column of the s block. Its ground-state electron configuration is [Ar]4s².
As a group 2 element, calcium has two valence electrons in its highest energy level, which occupy the 4s orbital. The complete electron configuration of calcium is 1s²2s²2p⁶ 3s² 3p⁶ 4s². When calcium forms a cation by losing these two valence electrons, it achieves a noble gas electron configuration similar to argon, becoming a Ca²⁺ ion.