Final answer:
The correct electronic configuration for gadolinium is [Xe] 4f⁷ 5d¹ 6s², making the answer (d). Gadolinium's half-filled 4f subshell contributes to its electronic stability.
Step-by-step explanation:
The electronic configuration of gadolinium (atomic number 64) can be determined by following the Aufbau principle, which includes filling the orbitals in order of increasing energy. For gadolinium, the correct electronic configuration is [Xe] 4f⁷ 5d¹ 6s², which makes the answer (d). Gadolinium has a half-filled 4f subshell, which adds stability to its electronic structure. The general order in which orbitals are filled is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d. While exceptions do occur, in the case of gadolinium, the electron fills the 4f subshell up to seven electrons before the 5d subshell begins to fill.
Additionally, it's important to remember that when forming ions, especially for transition metals and lanthanides like gadolinium, electrons are typically lost from the outermost s and then d or f orbitals. In the case of the Gd³+ ion, three electrons would be lost from the 6s and 5d orbitals, not the 4f orbitals, leaving the configuration as [Xe] 4f⁷.