Which one of the following compounds is more reactive towards `S_(N)2` reaction and why ? `CH_3CH(Cl) CH_2CH_3 or CH_3CH_2CH_2Cl`

Explanation

`CH_3overset(Cl)overset(|)CH-underset((a)(2^@))CH_2CH_3`
`underset((b)(1^@))(CH_3CH_2CH_2Cl`
Primary alkyl halides are more reactive towards `SN_2` reaction because primary alkyl halides are less hindered by alkyl groups rather than `2^@ or 3^@` which are having one more bulky groups which create hindrance for halogen to get detached.