Step 1: Basis of classification. Amines are classified as primary ($1^\circ$), secondary ($2^\circ$), or tertiary ($3^\circ$) based on the number of carbon atoms (alkyl or aryl groups) directly bonded to the nitrogen atom. Step 2: Classify structure (i): N,N-dimethyl-2-naphthylamine. The nitrogen in this compound is bonded to three carbon groups: two methyl ($-CH_3$) groups and the carbon of the naphthyl ring. It has no N-H bonds. It is a tertiary ($3^\circ$) amine. Step 3: Classify structure (ii): 2-naphthylamine. The nitrogen is bonded to only one carbon atom (from the naphthyl ring) and carries two N-H bonds. It is a primary ($1^\circ$) amine. Step 4: Summary. (i) N,N-dimethyl-2-naphthylamine is a tertiary ($3^\circ$) amine (N bonded to 3 carbon groups). (ii) 2-naphthylamine is a primary ($1^\circ$) amine (N bonded to 1 carbon group).
