Which of the Half-Reactions Below Would Be Complementary, Balance the Following

Which of the half-reactions below would be complementary, balance the following half-reaction, and be chemically reasonable? Br2 → 2 Br-

A) 2 K → 2 K+
B) K+ → K
C) K → K+
D) 2 K+ → 2 K
E) K → K+2