What is the IUPAC name of H2N–CH2–CH2–NH2?

The correct answer is Option (3) → Ethane-1,2-diamine

When a chain carries more than one amino group, the carbon atoms bearing –NH₂ are numbered, the prefix di (tri …) is put before “amine”, and the ‘e’ of the hydrocarbon name is kept. Here the two –NH₂ groups are on carbons 1 and 2 of ethane: ethane + 1,2 + diamine.

Why the other options are incorrect

Option (1) Ethan-1,2-diamine — Incorrect. The ‘e’ of ethane is dropped only in the name of a monoamine (ethanamine); before “diamine” it is retained.

Option (2) Ethane-1,1-diamine — Incorrect. This name puts both –NH₂ groups on the same carbon, \( \ce{CH3CH(NH2)2} \), a different compound.

Option (4) Ethane-1,2-amine — Incorrect. Two amino groups need the multiplying prefix di, so the ending must be “diamine”.

NCERT (2026-27 edition):
9.3 Nomenclature – “…In case, more than one amino group is present at different positions in the parent chain, their positions are specified by giving numbers to the carbon atoms bearing –NH₂ groups and suitable prefix such as di, tri, etc. is attached to the amine. The letter ‘e’ of the suffix of the hydrocarbon part is retained. For example, H₂N–CH₂–CH₂–NH₂ is named as ethane-1, 2-diamine.”