What is the ground-state electron configuration of gallium (Ga), written using noble-gas shorthand?

• A. $\left[Ar\right]4^{s}24^{p}3$
• B. $\left[Ar\right]4^{s}23^{d}104^{p}1$
• C. $\left[Ar\right]4^{s}23^{d}94^{p}2$
• D. $\left[Kr\right]5^{s}24^{d}105^{p}1$

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of gallium (Ga), which is 31. This tells us the total number of electrons to place in the electron configuration.
2. Recall the noble gas that precedes gallium in the periodic table, which is argon (Ar) with atomic number 18. Use this as the shorthand to represent the first 18 electrons: \([\mathrm{Ar}]\).
3. Determine the order of filling for the remaining electrons beyond argon. After argon, electrons fill the 4s orbital first, then the 3d orbitals, and finally the 4p orbitals.
4. Assign the electrons to these orbitals following the Aufbau principle: 2 electrons fill the 4s orbital, then 10 electrons fill the 3d orbitals, and the remaining electrons go into the 4p orbitals.
5. Write the full noble-gas shorthand electron configuration for gallium as \([\mathrm{Ar}]\,4s^{2}\,3d^{10}\,4p^{1}\), reflecting the correct distribution of all 31 electrons.