Greenish-Yellow colour gas, \(X\)with pungent smell and suffocating odour is produced when \(KMnO_4\) reacts with \(HCl\). \(X\)on reaction with excess \(NH_3\) forms \(Y\) and \(Z\). \(X\) on reaction with \(I_2\) in water forms \(HCl\) and an oxoacid of iodine, \(W\). Identify \(X, Y, Z, W\).
| \(X\) | \(Y\) | \(Z\) | \(W\) | |
| (1) | \(Cl_2\) | \(N_2\) | \(NH_4Cl\) | \(HIO_3\) |
| (2) | \(F_2\) | \(N_2\) | \(NH_4F\) | \(HIO_4\) |
| (3) | \(Cl_2\) | \(NCl_3\) | \(HCl\) | \(HIO_3\) |
| (4) | \(Cl_2\) | \(NCl_3\) | \(N_2\) | \(HIO_3\) |
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1
X: potassium permanganate oxidises hydrochloric acid to chlorine, a greenish yellow gas with a pungent, suffocating odour:
\( \ce{2KMnO4 + 16HCl -> 2KCl + 2MnCl2 + 8H2O + 5Cl2} \)
Y and Z: with excess ammonia, chlorine gives nitrogen and ammonium chloride (with excess chlorine it would give \( \ce{NCl3} \) instead):
\( \ce{8NH3 (excess) + 3Cl2 -> 6NH4Cl + N2} \)
W: chlorine water oxidises iodine to iodic acid, \( \ce{HIO3} \), and HCl:
\( \ce{I2 + 6H2O + 5Cl2 -> 2HIO3 + 10HCl} \)
So X = \( \ce{Cl2} \), Y = \( \ce{N2} \), Z = \( \ce{NH4Cl} \) and W = \( \ce{HIO3} \), which is row (1).
Why the other options are incorrect
Option (2) — Incorrect. \( \ce{KMnO4} \) cannot oxidise HCl to \( \ce{F2} \); fluorine is the strongest oxidising agent and is never liberated this way. The oxoacid formed is \( \ce{HIO3} \), not \( \ce{HIO4} \).
Option (3) — Incorrect. \( \ce{NCl3} \) forms only with excess chlorine; with excess ammonia the products are \( \ce{N2} \) and \( \ce{NH4Cl} \), and HCl is not left free because the excess \( \ce{NH3} \) takes it up as \( \ce{NH4Cl} \).
Option (4) — Incorrect. \( \ce{NCl3} \) and \( \ce{N2} \) are not formed together; with excess ammonia the products are \( \ce{N2} \) and \( \ce{NH4Cl} \).
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):
Chlorine – “… With excess ammonia, chlorine gives nitrogen and ammonium chloride whereas with excess chlorine, nitrogen trichloride (explosive) is formed.”
\( \ce{8NH3 + 3Cl2 -> 6NH4Cl + N2} \)