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.

How many different structural isomers that correspond to the molecular formula $C_3H_9N$ are possible? Out of these, how many will give a positive carbylamine test?

4 and 2

The correct answer is Option (3) → 4 and 2

There are four structural isomers for the molecular formula C₃H₉N:

1. Propan-1-amine (CH₃CH₂CH₂NH₂) — primary amine
2. Propan-2-amine (CH₃CH(NH₂)CH₃) — primary amine
3. N-Methylethanamine (CH₃CH₂NHCH₃) — secondary amine
4. N,N-Dimethylethanamine or trimethylamine ((CH₃)₃N) — tertiary amine

The carbylamine test (reaction with CHCl₃ and alcoholic KOH to give foul-smelling isocyanide) is positive only for primary amines (both aliphatic and aromatic). Secondary and tertiary amines do not give this test.

Thus, out of the four isomers, only the two primary amines (propan-1-amine and propan-2-amine) give a positive carbylamine test.