Which characteristic of the element Cobalt (Co) is most closely related to its chemical reactivity?

Question

A. Cobalt's two valence electrons

B. Cobalt's metallic properties including luster and conductivity

C. the 27 protons in the nucleus of Cobalt

D. Cobalt's non metallic properties including being brittle and dull

Answer 1

A. Cobalt's two valence electrons