What is the ground-state electron configuration of gallium (Ga, atomic number 31) using noble-gas shorthand?

• A. $\left[Ar\right]4^{s}23^{d}104^{p}1$
• B. $\left[Ne\right]3^{s}23^{p}64^{s}23^{d}104^{p}1$
• C. $\left[Ar\right]4^{s}23^{d}94^{p}2$
• D. $\left[Kr\right]4^{d}105^{s}25^{p}1$

Answer: (A)

Verified step by step guidance

1. Identify the atomic number of gallium (Ga), which is 31. This means gallium has 31 electrons to arrange in its electron configuration.
2. Start with the noble gas that precedes gallium in the periodic table to use as shorthand. Find the noble gas with the closest lower atomic number than 31. This noble gas will represent the core electrons.
3. Write the electron configuration of the noble gas in brackets. For gallium, this is argon (Ar), which accounts for the first 18 electrons.
4. Add the remaining electrons after the noble gas configuration by filling the orbitals in order of increasing energy: first the 4s orbital, then the 3d orbital, and finally the 4p orbital. Remember the order of filling is 4s before 3d.
5. Distribute the remaining electrons accordingly: 2 electrons in 4s, 10 electrons in 3d, and 1 electron in 4p to complete the ground-state electron configuration of gallium using noble-gas shorthand.