Answer the question on the basis of passage given below:
Nitrogen forms a large number of oxoacids such as \(H_2N_2O_2\) (hyponitrous acid), \(HNO_2\) (nitrous acid) and \(HNO_3\) (nitric acid). Amongst these, \(HNO_3\) is the most important. It is used in the manufacture of ammonium nitrate for fertilisers and other nitrates for use in explosives. It is also used to prepare many important organo-nitro compounds like nitroglycerine, trinitrotoluene etc. It acts as a strong oxidizing agent and used as an oxidiser in rocket fuels.
The covalency and oxidation state of nitrogen in \(HNO_3\), are:-
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → four and +5, respectively
Covalency is the number of covalent bonds an atom forms (shared electron pairs, a coordinate bond included), whereas the oxidation state is the charge the atom would carry if all its bonds were ionic. The two need not be equal.
Nitrogen has only four valence orbitals (one 2s and three 2p) and no d orbitals, so its maximum covalency is 4. In \( \ce{HNO3} \), N forms a single bond to the OH group, a double bond to one O and a coordinate bond to the other O (N→O): 1 + 2 + 1 = 4 bonds.
Oxidation state of N in \( \ce{HNO3} \), with H = +1 and O = −2:
\( 1 + x + 3(-2) = 0 \Rightarrow x = +5 \)
So the covalency is four and the oxidation state is +5.
Why the other options are incorrect
Option (1) five and +5, respectively — Incorrect. A covalency of five would need a fifth orbital (a d orbital), which nitrogen does not have; this is why the structure is drawn with an N→O coordinate bond, not two N=O double bonds.
Option (3) five and +4, respectively — Incorrect. Both values are wrong; +4 is the oxidation state of N in \( \ce{NO2} \), not in \( \ce{HNO3} \).
Option (4) four and +4, respectively — Incorrect. The covalency is right, but the charge balance above gives +5, not +4.
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):
Anomalous Properties of Nitrogen – “… Nitrogen is restricted to a maximum covalency of 4 since only four (one s and three p) orbitals are available for bonding.”