(i) 4-Bromo-4-methylpent-2-ene                   3° and Allylic halide
(ii) 1-Chloro-4-(2-methylpropyl) benzene      Aryl halide
(iii) 1-Chloromethyl-3-(2,2-dimethylpropyl)   Benzene Benzylic halide (1°)
(iv) 1-Bromo-2-(1-methylpropyl)benzene      Aryl halide

The IUPAC name of DDT is 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane. The IUPAC name of bezenehexachloride is 1,2,3,4,5,6-hexachlorocyclohexane. Their use is banned in India and other countries because DDT is not metabolised very rapidly or solubilized effectively by animals.

(iii) 2-Bromo-2 methylpropane will react with aq KOH most easily because it will form 3^o carbocation which is most stable.

The functional group is ortho and para directing because electron density is maximum at ortho and partho para-positions.

(b) will not react due to presence of double bond character in C---- O bond due to resonance.

It is because iodination is reversible as HI formed is good reducing agent which needs to be removed with the help of oxidising agent.

Haloarenes are resonance stabilized. Due to resonance, C-X bond in haloarenes acquire a double bond character which makes them more stable than haloalkanes.

The reaction is an S_N2 reaction. In this reaction, CN- acts as the nucleophile and attacks the carbon atom to which Br is attacked. CN- is an ambident nucleophile and can attack through both C and N. In this case, it attacks through the C-atom.

Ambident Nucleophile- An anionic nucleophile, which has two nucleophilic centers, or two negative sites is known as an ambident nucleophile. This negative charge is delocalized due to resonance.
Example – Cyanide and Thiocyanate are examples of ambident nucleophiles. 
^-C≡N   ↔   :C=N^-
S=C=N^- ↔  ^-S - C≡ N