Question

which is the correct electron configuration for the element phosphorus?
$1s^2 2s^2 2p^6 3s^2 3p^6$
$1s^2 2s^2 2p^6 3s^2 3p^3$
$1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}$
$1s^2 2s^2 2p^6 3s^2 3p^2$

Explanation:

Phosphorus has an atomic number of 15, meaning it has 15 electrons. We fill orbitals in order of increasing energy: 1s (holds 2), 2s (2), 2p (6), 3s (2), then the remaining 3 electrons go to 3p. Adding these: 2+2+6+2+3=15, matching the total electrons.

Answer:

1s² 2s² 2p⁶ 3s² 3p³