Read the passage carefully and answer.
Organic compounds derived from \( NH_3 \) by replacing one or more H-atoms with alkyl or aryl groups will form primary, secondary and tertiary amines. The common methods which include their preparations are reduction of nitro group, amide group and nitrile group, Gabriel phthalimide synthesis and ammonolysis of alkyl halides. Amines are basic in nature due to the presence of a lone pair of electrons on the nitrogen atom. Important chemical properties of amines include acylation, alkylation and their interaction with nitrous acid. There are various tests which can distinguish different types of amines from each other, for e.g. carbylamine test, Hinsberg's test, coupling reaction etc. Another important class of compounds which can be derived from primary amines is azo compounds. These compounds are intensely colored and widely used as dyes in textile, leather and food industries.
Conversion of nitro group into primary amine is preferred using
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(Fe\) and \(HCl\)
A nitro group is reduced to a primary amino group either by catalytic hydrogenation (hydrogen gas over finely divided nickel, palladium or platinum) or by a metal in acidic medium (Sn/HCl or Fe/HCl). Six hydrogen atoms are added and two molecules of water are lost:
\( \displaystyle \ce{C6H5NO2 + 6[H]} \xrightarrow{\ce{Fe/HCl}} \ce{C6H5NH2 + 2H2O} \)
The iron(II) chloride formed in the reaction is hydrolysed and gives back hydrochloric acid:
\( \displaystyle \ce{FeCl2 + 2H2O -> Fe(OH)2 + 2HCl} \)
Why the other options are incorrect
Option (2) \(Sn\) and \(HCl\) — Incorrect. Tin and hydrochloric acid also reduce the nitro group, but the acid is used up during the reaction, so a large amount of acid (and costly tin) is needed.
Option (3) \(Pt-H_2\) — Incorrect. Catalytic hydrogenation over platinum works, but it needs hydrogen gas and an expensive catalyst; it is not the method the book names as preferred.
Option (4) \(Pd-H_2\) — Incorrect. Hydrogenation over palladium has the same drawback as over platinum: hydrogen gas and a costly noble-metal catalyst.
NCERT (2026-27 edition):
Reduction of Nitro Compounds
