Which of the Following Statements Best Explains Why Potassium (K)

Which of the following statements best explains why potassium (K) reacts easily with bromine (Br) ?

A) Potassium and bromine both have valence electrons in the fourth energy level.
B) Potassium and bromine have the same number of electrons in their highest energy levels.
C) Potassium has one electron in its highest energy level, and bromine needs one electron to complete its highest energy level.
D) Potassium needs one electron to complete its highest energy level, and bromine has an extra electron in its highest energy level.