Following compounds are given to you :
2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane
(i) Write the compound which is most reactive towards `S_(N) 2` reaction
(ii) Write the compound which is optically active
(iii) Write the compound which is most reactive towards `beta`-elimination reaction

Explanation

`overset(" 2Bromopentane")(C-C-C-overset(Br)overset(|)(C) -C) " " overset("2-Bromo-2-methylbutane")(C-C-underset(underset(Br)(|))overset(overset(CH_(3))(|))(C) - C) " " overset("1-Bromopentane")(C-C-C-C-C-Br)`
(i) 1-Bromopentane is most reactive twoards `S_(N)2` reactin because it is `1^(@)` alkylhalide.
(ii) 2-Bromopentane is optically active because it is having chiral carbon (attached with four different groups)

(iii) 2-Bromo-2-methylbutane is most reactive towards `beta-`elimination reaction because it gives a more stable (highly substituted) alkene.
`H_(3) C - CH_(2) -underset(underset(CH_(3))(|))overset(Br)overset(|)(C) - CH_(3) overset(KOH (alc.))rarr H_(3)C - underset("(highly substituted alkene)")(H_(2) C - underset(CH_(3))underset(|)(C) = CH_(2))`