JEE Main 2021 · 18 March · evening · Single correct · +4 / −1

The oxidation states of nitrogen in NO, NO₂, N₂O and NO₃ - are in the order of :

  1. (a) N₂O > NO₂ > NO > NO₃ -
  2. (b) NO > NO₂ > N₂O > NO₃ -
  3. (c) NO₂ > NO₃ - > NO > N₂O
  4. (d) NO₃ - > NO₂ > NO > N₂O
Answer and solution

Answer (d) NO₃ - > NO₂ > NO > N₂O

Solution

Chemistry ma’am · 3 steps

Oxygen is always -2 here, so let the oxygens fix nitrogen's number in each species one by one.

  1. The rule. Oxygen takes -2 in all four species. The oxidation numbers in a species must add up to its overall charge: zero for a neutral molecule, -1 for NO₃⁻.
    SpeciesEquation for NOxidation state of N
    NO₃⁻x + 3(-2) = -1+5
    NO₂x + 2(-2) = 0+4
    NOx + (-2) = 0+2
    N₂O2x + (-2) = 0+1
  2. Two nitrogens. In N₂O there are two nitrogen atoms sharing the +2 that balances one oxygen. So each nitrogen is only +1, not +2.
  3. So. The order is +5 > +4 > +2 > +1, that is NO₃⁻ > NO₂ > NO > N₂O. This matches option (d).

The idea to keep. Write one small equation per species: the oxidation numbers add up to the overall charge. Divide by the number of central atoms, and remember the ion's charge.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Redox Reactions

Asked about 90 times in JEE Main since 2020. This question is from 2021.