Which electron configuration corresponds to bromine (Br, atomic number 35) in simplified noble-gas notation?

• A. $\left[Ar\right]4^{s}23^{d}104^{p}6$
• B. $\left[Ne\right]3^{s}23^{p}5$
• C. $\left[Kr\right]4^{d}105^{s}25^{p}5$
• D. $\left[Ar\right]4^{s}23^{d}104^{p}5$

Answer: (D)

Verified step by step guidance

1. Identify the atomic number of bromine (Br), which is 35. This means bromine has 35 electrons to arrange in its electron configuration.
2. Recall the noble gas that comes before bromine in the periodic table to use as the shorthand notation. The noble gas before bromine is argon (Ar), which has 18 electrons.
3. Write the electron configuration starting with the noble gas shorthand: \([\text{Ar}]\). This accounts for the first 18 electrons.
4. Add the electrons beyond argon by filling the next orbitals in order: 4s, 3d, and 4p. According to the Aufbau principle, the order is 4s, then 3d, then 4p.
5. Distribute the remaining electrons (35 - 18 = 17) into these orbitals: 2 electrons in 4s, 10 electrons in 3d, and the remaining 5 electrons in 4p. This gives the configuration \([\text{Ar}]\,4s^{2}\,3d^{10}\,4p^{5}\).