Final answer:
Valence electrons are the electrons in the outermost shell of an atom. Phosphorus has 5 valence electrons with the electron configuration '3s²3p³'.
Step-by-step explanation:
The question asks about valence electrons and their configuration within an atom. To determine this, one should look at the highest energy levels in the electron configuration of an atom, as valence electrons reside in the outermost energy level or shell. For example, in the case of the phosphorus (P) atom mentioned as having a valence electron configuration of '3s23p3', it has a total of 5 valence electrons because there are two electrons in the 3s subshell and three electrons in the 3p subshell.