Cobalt (Co) has 9 valence electrons. The electron configuration of cobalt is [Ar] 3d^7 4s^2, where [Ar] represents the electron configuration of the noble gas argon. In the outermost energy level, the 4s orbital contains 2 electrons, and the 3d orbital contains 7 electrons. Therefore, the total number of valence electrons for cobalt is 9.