Zinc metal reacts with dilute nitric acid to liberate gas:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → N2O
Nitric acid is a strong oxidising agent, and the reduction product depends on the concentration of the acid, the temperature and the metal. A very reactive metal such as zinc reduces dilute \( \ce{HNO3} \) further than copper does: N goes from +5 to +1 (\( \ce{N2O} \)). With concentrated acid the product is \( \ce{NO2} \) (+4).
\( \displaystyle \ce{4Zn + 10HNO3 (dilute) -> 4Zn(NO3)2 + 5H2O + N2O} \)
\( \displaystyle \ce{Zn + 4HNO3 (conc.) -> Zn(NO3)2 + 2H2O + 2NO2} \)
Why the other options are incorrect
Option (1) NO2 — Incorrect. This is given by concentrated nitric acid (with Zn and also with Cu).
Option (3) NO — Incorrect. Nitric oxide is the product of copper with dilute nitric acid:
\( \displaystyle \ce{3Cu + 8HNO3 (dilute) -> 3Cu(NO3)2 + 2NO + 4H2O} \)
Option (4) N2O3 — Incorrect. Dinitrogen trioxide (N in +3) is not a product of the action of metals on nitric acid; it is prepared from NO and \( \ce{N2O4} \) at about 250 K.
\( \displaystyle \ce{2NO + N2O4} \xrightarrow{\text{250 K}} \ce{2N2O3} \)
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):
Properties – “… 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.
\( \ce{3Cu + 8HNO3(dilute) -> 3Cu(NO3)2 + 2NO + 4H2O} \)
\( \ce{Cu + 4HNO3(conc.) -> Cu(NO3)2 + 2NO2 + 2H2O} \)
Zinc reacts with dilute nitric acid to give N2O and with concentrated acid to give NO2.
\( \ce{4Zn + 10HNO3(dilute) -> 4Zn(NO3)2 + 5H2O + N2O} \)
\( \ce{Zn + 4HNO3(conc.) -> Zn(NO3)2 + 2H2O + 2NO2} \)”