Question

Which element has exactly five electrons in the highest principal energy level (the outer shell)?
a. B
b. Ba
c. P
d. Mn

Answer 1

This question is asking for an element with 5 valence electrons.  Just go to the row it is in (excluding transition metals) and count over.  
The answer would be c. P

Answer 2

Phosphorus (P) has 5 valence electrons in its outer shell, meaning, it needs 3 more to become a stable element.