* Roman numerals in chemical names indicate oxidation state. In this case, "IV" means nitrogen has an oxidation state of +4.

* Nitrogen can have multiple oxidation states. The most common oxides of nitrogen are:

* Nitrogen monoxide (NO): Nitrogen has an oxidation state of +2.

* Nitrogen dioxide (NO₂): Nitrogen has an oxidation state of +4.

* Dinitrogen tetroxide (N₂O₄): This is a dimer of NO₂ and is also sometimes called nitrogen(IV) oxide.

* Dinitrogen pentoxide (N₂O₅): Nitrogen has an oxidation state of +5.

Therefore, the correct name for the compound with nitrogen in the +4 oxidation state is nitrogen dioxide (NO₂).