Final answer:
The name of the compound CoS is cobalt(II) sulfide, as it includes the cobalt with a 2+ charge, paired with sulfur with a 2- charge.
Step-by-step explanation:
The name of CoS is cobalt(II) sulfide. Cobalt can have more than one possible charge, and when naming compounds with such a metal, the charge must be included in the name to differentiate between the possible states. According to the rules for naming ionic compounds, which take into account multiple oxidation states, the proper name for CoS, where cobalt has a 2+ charge and sulfur a 2- charge, thereby balancing each other out, is cobalt(II) sulfide.