Step 1:

Amines are classified as primary (1^o ), secondary (2^o ) and tertiary (3^o ) depending upon the number of hydrogen atoms replaced by alkyl or aryl groups in ammonia molecule.

If one hydrogen atom of ammonia is replaced by R or Ar , we get RNH₂ or ArNH₂ , a primary amine (1^o ) is obtained.

If two hydrogen atoms of ammonia or one hydrogen atom of R-NH₂ are replaced by another alkyl/aryl(R’) group then  
R-NHR’, the secondary amine is obtained as a product.

If all the hydrogen atom is replaced by an alkyl/aryl group then tertiary amine is obtained as a product. 

Step 2:

(i)
The molecular formula of the given compound is (CH₃)₂CHNH₂ . The structure is as follows:


The parent chain contains three carbon atoms. The carbon-containing -NH₂ group gets the lowest position. The structure with the numbering is as follows:


The IUPAC name of the compound is propan-2-amine and the amine is primary because only one alkyl group is attached to a nitrogen atom.

(ii)
The molecular formula of the given compound is CH₃(CH₂)₂NH_2. The structure is as follows: 



The longest carbon chain contains three carbon atoms. The structure with numbering is as follows:

 

The IUPAC name of the compound is propanamine and the amine is primary because only one alkyl group is attached to a nitrogen atom.

(iii)
The molecular formula of the compound is CH₃NHCH(CH₃)₂. The structure of the compound is as follows:

The parent chain contains three carbon atoms. A methyl group is attached to a nitrogen atom. In the case of secondary and tertiary amines, use locant N to designate a substituent attached to a nitrogen atom. The structure with numbering is as follows:



Hence, the IUPAC name of the compound is N−methylpropan-2-amine and the amine is secondary because two alkyl groups are attached to a nitrogen atom.

(iv)
The molecular formula of the compound is (CH₃)₃CNH₂. The structure of the compound is as follows:



The parent chain contains three carbon atoms and a methyl group. The structure with numbering is as follows:


The IUPAC name of the compound is 2-methylpropan-2-amine and the amine is primary because only one alkyl group is attached to the nitrogen atom.

(v)
The molecular formula of the compound is C₆H₅NHCH₃.  The structure is as follows:



When the benzene ring contains a -NH₂ group then it is known as benzamine. The methyl group is attached to the nitrogen atom. Hence, the IUPAC name of the compound is N−Methylbenzamine and the amine is secondary because two alkyl groups are attached to a nitrogen atom.

(vi)
The molecular formula of the compound is (CH₃CH₂)₂NCH₃. The structure is as follows:



The parent chain contains two carbon atoms, ethyl, and a methyl group is attached to the nitrogen atom. The compound with a numbering system is as follows:


The IUPAC name of the compound is N-Ethyl-N-methylethanamine and the amine is tertiary because three alkyl groups are attached to a nitrogen atom.

(vii)
The molecular formula of the compound is m–BrC₆H₄NH₂. The structure is as follows:


The NH₂ group gets a higher priority than Br. Hence, the IUPAC name of the compound is 3-bromobenzamine and  the amine is primary because only one alkyl group is attached to the nitrogen atom.