Correct Answer - B
This is nucleophilic substitution
`CH_(3)underset(3^(@)amine)(CH_(2)NH_(2))overset(CH_(3)Br)rarrCH_(3)underset(2^(2)amine)(CH_(3)CH_(2)NHCH_(3)overset(CH_(3)Br)rarr`
`CH_(3)underset(3^(@)amine)(CH_(2))N(CH_(3))_(2)overset(CH_(3)Br)rarrunderset("Quaternary ammonium salt")(CH_(3)CH_(2)overset(+)N(CH_(3))_(3)Brbar` .