Why is Mo(II)nitride = MoN3 and not M02N3

Question

Also

Why is PbO2 not Pb2O4

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Answer 1

For Mo2N3 N would need to be -2 oxidation state and that is highly unlikely. N has usual oxidation states of -3, +3, and +5. Mo has several including 2,3,4,5, and 6.

For PbO2, we usually write the empirical formula unless there is evidence that it exists in some other form; i.e., HO is the empirical formula for hydrogen peroxide BUT we know it exists as H2O2 and we write it the way it exists.