Arrange in order of reactivity towards `S_(N)2` reactions:
(2) 1-bromo-3-methyl butane,2-bromo-2-methylbutane, 2-bromo-3methylbutane

Explanation

`S_(N)2` reactivity decreases as `1^(@) > 2^(@) > 3^(@)` (because steric hindrance at the `alpha` -carbon increases in this sequence).
`underset(1-"bromo-3-methylbutane")(CH_(3)-underset((A))overset(CH_3)overset(|)(C)H-CH_(2)overset(alpha)(C)H_(2)=Br)` `underset(2-"bromo-2-methylbutane" (3^@))(CH_(3)-CH_(2)-underset(Br_((B)))underset(|)overset(CH_(3))(C^alpha)-CH_(3))`
`CH_(3)-underset(C)overset(CH_(3))overset(|)(.^(o+)C)-underset(Br)underset(|)overset(alpha)(C)H- underset(2-bromo-3-"methylbutane"(2^(@)))(CH_(3))`
Thus, the sequence of `S_(N)2` reacitivity is A > C > B.