Question

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identify the complete electron configuration for an atom of
the element beryllium (be):
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$1s^{2}1p^{2}$
$1s^{2}$
$2s^{2}2p^{2}$
$1s^{2}2p^{2}$
$1s^{2}2s^{2}$
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Explanation:

Step1: Find Be's atomic number

Beryllium (Be) has an atomic number of 4, so it has 4 electrons.

Step2: Follow Aufbau principle

Fill orbitals in order: 1s, 2s, 2p... The 1s orbital holds max 2 electrons, then fill 2s.
$$1s^2 2s^2$$
This accounts for all 4 electrons. Eliminate options with non-existent $1p$ orbitals, or incomplete/incorrect orbital filling.

Answer:

1s² 2s²