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.
Which of the following behaves as the strongest oxidising agent?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(HNO_3\)
The oxidising power of an oxoacid of nitrogen rises with the oxidation state of nitrogen: the higher the oxidation state, the more strongly the acid takes electrons. Working out the oxidation state x of N in each compound (H = +1, O = −2):
\( \ce{HNO3} \): 1 + x + 3(−2) = 0, so x = +5
\( \ce{HNO2} \): 1 + x + 2(−2) = 0, so x = +3
\( \ce{H2N2O2} \): 2 + 2x + 2(−2) = 0, so x = +1
\( \ce{NH3} \): x + 3 = 0, so x = −3
Nitrogen is in its highest oxidation state (+5) in nitric acid, which is a strong oxidising agent that attacks most metals and also oxidises non-metals (iodine to iodic acid, carbon to \( \ce{CO2} \), sulphur to \( \ce{H2SO4} \)).
Why the other options are incorrect
Option (1) \(HNO_2\) — Incorrect. Nitrogen is only +3 here, a middle oxidation state; nitrous acid can act as an oxidising agent or a reducing agent, and it is the weaker oxidant of the two acids.
Option (3) \(NH_3\) — Incorrect. Nitrogen is in its lowest oxidation state (−3) and cannot gain more electrons; ammonia acts as a reducing agent (it reduces CuO to Cu on heating), not as an oxidising agent.
Option (4) \(H_2N_2O_2\) — Incorrect. In hyponitrous acid nitrogen is only +1, so its oxidising power is much lower than that of nitric acid.
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):
Nitric Acid – “… Concentrated nitric acid is a strong oxidising agent and attacks most metals except noble metals such as gold and platinum. The products of oxidation depend upon the concentration of the acid, temperature and the nature of the material undergoing oxidation.”