Question

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identify the complete electron configuration for an atom of
the element aluminum (al):

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$2s^{2}2p^{6}3s^{2}3p^{1}$
$1s^{2}2s^{2}3s^{2}3p^{1}$
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$
$1s^{2}2s^{2}2p^{6}3p^{3}$
$1s^{2}2p^{6}3p^{3}$
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Explanation:

Step1: Find Al's atomic number

Aluminum (Al) has an atomic number of 13, so it has 13 electrons.

Step2: Follow Aufbau principle

Fill orbitals in order: $1s, 2s, 2p, 3s, 3p$. $1s$ holds 2, $2s$ holds 2, $2p$ holds 6, $3s$ holds 2, remaining 1 goes to $3p$.
<Expression>
$1s^2 2s^2 2p^6 3s^2 3p^1$
</Expression>

Step3: Match with options

Compare the derived configuration to the given choices.

Answer:

$1s^2 2s^2 2p^6 3s^2 3p^1$ (the third option)