Write the structures of the following organic halogen compounds:
1, 4–Dibromobut-2-ene.

Arrange the nucleophilicity (rate of S_N2 reactivity) of 
(i) H₂O, OH–, CH₃COO^- and CH₃O^-

(ii) NH₃ and PH₃.

Arrange the following compounds according to their relative reactivity with the reagents mentioned against them.

(a)    C₆H₅CH₂CH₂Br, C₆H₅CHBrCH₃ and C₆H₅CH = CHBr with alcoholic silver nitrate.

(b)    C₆H₅CH₂Br, n-C₆H₁₃ Br and C₆H₅Br with ale. AgNO₃ or with KCN.

(c)    t-Butyl chloride, sec-butyl chloride and CCl₄ with ale. silver nitrate.

(d)    m-Nitro chlorobenzene, 2, 4-dinitro-chlorobenzene and p-nitro chlorobenzene with sodium ethoxide.