Which half-reaction correctly describes an oxidation?
A
Upper C a (s) plus 2 e superscript minus right arrow upper C a superscript 2 plus (a q).
B
Upper B r subscript 2 plus 2 e superscript minus right arrow 2 upper B r superscript minus.
C
Upper N a superscript plus (a q) right arrow upper N a (s) plus e superscript minus.
D
Upper C r (s) right arrow upper C r superscript 3 plus (a q) plus 3 e superscript minus.