What is the name of the Co3N2 molecule? ۔
Cobalt is a versatile metal. So you need to add the oxidation state to the name ...
N 3 ... 2x3 = 6.
There are 3 Cos, so +6/3 = +2 ... that is, all Co must be in the +2 state so that this molecule can be neutralized.
Cobalt (II) nitride.
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Nitrogen usually adopts an oxidation state 3 when combined with more electropositive elements. In this case, the total oxidation number of nitrogen is 6 and the total oxidation number of cobalt should also be +6, so all cobalt is +2. The name there must be cobalt (II) nitride in the stock system.