Which of the following is the correct electron configuration for beryllium (Be)?

• A. 1s^2 2s^1
• B. 1s^2 2s^2
• C. 1s^2 2p^1
• D. 1s^2 2p^2

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of beryllium (Be), which tells you the total number of electrons. Beryllium has an atomic number of 4, so it has 4 electrons.
2. Recall the order in which electron orbitals are filled according to the Aufbau principle: electrons fill orbitals starting from the lowest energy level to higher ones. The order begins with 1s, then 2s, then 2p, and so on.
3. Distribute the 4 electrons into the orbitals following the order: fill the 1s orbital first, which can hold up to 2 electrons, then move to the 2s orbital.
4. Since 1s can hold 2 electrons, place 2 electrons there. The remaining 2 electrons will go into the 2s orbital, which can also hold up to 2 electrons.
5. Write the electron configuration by listing the orbitals and the number of electrons in each: \$1s^2 2s^2$. This matches the correct electron configuration for beryllium.