Q.Ethane-1, 2-diamine is —

Ethane-1,2-diamine has an –NH2 group on carbon 1 AND carbon 2 of the two-carbon (ethane) chain.

The IUPAC name 'ethane-1,2-diamine' is read as: ethane (a 2-carbon chain, C1–C2) + di + amine, with the locants 1,2 telling us WHERE the two –NH2 groups sit — one on C1 and one on C2. That structure is H2N–CH2–CH2–NH2 (also called ethylenediamine, 'en', a well-known bidentate ligand). The other options either have only …

For a secondary amine R-NH-R', the IUPAC name picks the LARGER group as the parent 'alkanamine' chain and cites the smaller group as an N-substituent prefix.

CH3-NH-CH2-CH3: the nitrogen is bonded to a methyl group (CH3-) and an ethyl group (CH3CH2-).

The larger/senior chain is ethyl (2 carbons), so the parent amine is ethanamine (CH3CH2NH2 in unsubstituted form). The methyl group attached to nitrogen becomes an N-substituent, cited with the italic locant N-:

Name: N-Methylethanamine

…

A secondary amine has its nitrogen bonded to exactly two carbon (alkyl/aryl) groups and one hydrogen.

Propan-2-amine, CH3-CH(NH2)-CH3, has N bonded to one alkyl group and two H atoms - a primary amine.

Pentan-3-amine similarly has N bonded to one alkyl carbon and two H atoms - a primary amine. …

Amines are classified by how many hydrogens of NH3 are replaced by alkyl/aryl groups; a primary amine replaces just one, giving RNH2.

Amines are derivatives of ammonia (NH3) formed by replacing one, two, or three H atoms with alkyl/aryl groups:

• Primary (1 degree) amine: one H replaced, RNH2, e.g. CH3NH2 (methanamine), C6H5NH2 (aniline).
• Secondary (2 degree) amine: two H's replaced, R2NH, e.g. (CH3)2NH (dimethylamine). …

The compound is a tertiary amine with a sec-butyl group and two methyl groups on nitrogen; IUPAC substitutive nomenclature names it as 2-(N,N-dimethylamino)butane.

sec-Butyl is $CH_3CH_2CH(CH_3)-$, attached through its C-2. In 'dimethyl sec-butylamine', both methyl groups and the sec-butyl group are on the same nitrogen: $(CH_3)_2N-CH(CH_3)CH_2CH_3$. Treating the four-carbon chain (butane) as the parent and the $-N(CH_3)_2$ group as an (N,N-dimethylamino) substituent at C-2 gives the IUPAC name 2-(N,N-dimethylamino)butane. Option (a) describes a diamine-type name for a differen …