Arrange the folliwing compounds in increasing order of `SN^(-2)` reactivity.
a. I.m `ClCH_(2)CH = CHCH_(2)CH_(3)`
II. `CH_(3)C(Cl) = CHCH_(2) CH_(3)`
III. `CH_(3)CH = CHCH_(2)CH_(2)Cl`
IV. `CH_(3)CH = CHCH_(2)(Cl) CH_(3)`
b. I. `CH_(3)CH_(2)Br`
II. `CH_(2) = CHCH(Br) CH_(3)`
III. `CH_(2) = CHBr`
IV. `CH_(3)CH (Br) CH_(3)`
C. I. `(CH_(3))_(3)CCl`, II. `C_(6)H_(5)C(CH_(3))_(2)Cl`
III. `(CH_(3))_(2)CHCl`, IV. `CH_(3)CH_(2)CH_(2)Cl`

Explanation

c. `(II) gt (I) gt (III) gt (IV)`
`Ph underset(CH_(3))underset(|)overset(CH_(3)) overset(|)(-C-) CH_(3) gt CH_(3) underset(CH_(3)) underset(|)overset(CH_(3))overset(|)(-C-) Cl gt CH_(3) underset(H) underset(|)overset(CH_(3)) overset(|)(-C-) Cl gt CH_(3) CH_(2) CH_(2) Cl`
Benzylic `C^(o+) gt 3^(@)c^(o+) gt 2^(@) C^(o+) gt 1^(@) C^(o+)`