Final answer:
Nitrogen is the smallest element in its family.
Step-by-step explanation:
To determine which element is the smallest in its family, we need to consider the number of valence electrons and the charge.
An atom with five valence electrons and a negative three charge means that it has gained three additional electrons, making the total number of electrons eight, which is the electron configuration of a noble gas.
Based on this information, we can conclude that the element with five valence electrons and a negative three charge is Nitrogen (option a).