Oxidation state of nitrogen in nitrite ion

Steps:

• In NO₂⁻, each O is -2 (total -4); ion charge -1, so N oxidation state = +3.
• In NH₄F (NH₄⁺ ion), each H is +1 (total +4); ion charge +1, so N = -3.
• In N₂O, O is -2; neutral molecule, two N total +2 (average +1).
• In NO₃⁻, three O total -6; ion charge -1, so N = +5; in NF₃, three F total -3; neutral, so N = +3.

Why D is correct:

• NF₃ follows the rule that F is always -1; thus, N must be +3 to balance the neutral molecule, identical to NO₂⁻.

Why the others are wrong:

• A: NH₄⁺ has N at -3 due to H's +1 oxidation states.
• B: N₂O's neutrality requires N atoms to average +1, not +3.
• C: NO₃⁻ has N at +5 from three O's -2 each.

Final answer: D