How many outer electrons does a boron atom have?

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A labeled diagram of the periodic table entry for boron shows its atomic number 5, symbol B, electron configuration, atomic weight range, and classification as a solid, weakly acidic, other nonmetal with a rhombohedral crystal structure at room temperature. — boron Properties of boron.

A boron atom has three outer electrons.1

As a member of the boron group (Group 13) of the periodic table, boron has an electron configuration of $1 s^{2} 2 s^{2} 2 p^{1}$ . The three electrons in the second shell (the $2 s^{2}$ and $2 p^{1}$ orbitals) constitute its valence, or outer, electrons. In the formation of covalently bonded compounds, one of the $2 s$ electrons is promoted to a $2 p$ orbital, resulting in an outer configuration of $2 s^{1} 2 p^{2}$ .12