In the given equations (Note : equations are not balanced)
\(Zn + \text{ conc. }HNO_3 \longrightarrow Zn(NO_3)_2 + x + H_2O\) -------(1)
\(Zn + \text{ Dil. }HNO_3 \longrightarrow Zn(NO_3)_2 + y + H_2O\) ---------(2)
The compounds \(x\) and \(y\) respectively are:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(NO_2 \text{ and } N_2O\)
Nitric acid is a strong oxidising agent, and the product it is reduced to depends on its concentration and on the metal. Concentrated acid is reduced only a little, to \( \ce{NO2} \) (N: +5 → +4). Dilute acid with a very active metal such as zinc is reduced further, to \( \ce{N2O} \) (N: +5 → +1).
So with the concentrated acid x = \( \ce{NO2} \), and with the dilute acid y = \( \ce{N2O} \).
So x and y are NO2 and N2O.
Why the other options are incorrect
Option (1) NO2 and NO — Incorrect. NO is the product of copper with dilute nitric acid (3Cu + \( \ce{8HNO3} \) → \( \ce{3Cu(NO3)2} \) + 2NO + \( \ce{4H2O} \)); zinc, being more reactive, reduces the dilute acid further, to \( \ce{N2O} \).
Option (2) NO2 and NO2 — Incorrect. \( \ce{NO2} \) is formed only with the concentrated acid; the dilute acid gives a product with nitrogen in a lower oxidation state.
Option (3) N2O and NO2 — Incorrect. This reverses the two products; \( \ce{N2O} \) comes from the dilute acid, \( \ce{NO2} \) from the concentrated 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 – …
