# Question #678ec

Since $Z = 13$, the electronic configuration of this element, which can be obtained using the principle of Aufbau, is $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{1}$.
That means that at the last level (the $n = 3$ level) there will be two paired electrons in the $3 s$ orbital and one solitary electron (and, therefore, necessarily unpaired) in one of the $3 p$ orbitals (in any of them since all three are degenerate).