Answer the question on the basis of the passage given below:
Molecular nitrogen is very little reactive chemically. During lightning discharge, atmospheric nitrogen and oxygen combine to form nitric oxide which also combines with oxygen to form nitrogen dioxide. Both \(NO\) and \(NO_2\) constitute smog which is very poisonous. It can cause a burning sensation in the eyes and adversely affect the respiratory system.
Oxidation state of nitrogen in nitric acid and Nitrogen dioxide respectively is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → +5, +4
The oxidation state of nitrogen is found by putting H = +1 and O = −2 and making the sum equal to the charge on the molecule (zero).
In nitric acid, \( \ce{HNO3} \):
\( (+1) + x + 3(-2) = 0 \Rightarrow x = +5 \)
In nitrogen dioxide, \( \ce{NO2} \):
\( x + 2(-2) = 0 \Rightarrow x = +4 \)
So nitrogen is +5 in HNO3 and +4 in NO2. This also explains why \( \ce{NO2} \) dissolves in water to give a mixture of \( \ce{HNO3} \) (+5) and \( \ce{HNO2} \) (+3): the +4 state disproportionates.
\( \ce{2NO2 + H2O -> HNO3 + HNO2} \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Oxides of Nitrogen – …
