Which of the following elements has a ground state electronic configuration with an incomplete penultimate shell?
Answer Details
The electronic configuration of an atom refers to the arrangement of electrons in its various shells or energy levels. The penultimate shell is the second-to-last shell of an atom. An incomplete penultimate shell means that the penultimate shell is not completely filled with electrons.
Out of the given options, Iron has a ground state electronic configuration with an incomplete penultimate shell. The electronic configuration of Iron (Fe) is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶. In this configuration, the 3d sub-shell is incomplete with 6 electrons, and the 4s sub-shell is complete with 2 electrons. Therefore, Iron has an incomplete penultimate shell.
Sodium, Aluminium, and Calcium all have complete penultimate shells in their ground state electronic configurations. Sodium (Na) has an electronic configuration of 1s² 2s² 2p⁶ 3s¹, Aluminium (Al) has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p¹, and Calcium (Ca) has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². In all of these configurations, the penultimate shell is complete, and thus none of these elements have an incomplete penultimate shell.
Therefore, the correct answer is Iron.