Which alkyl halide from the following pair is chiral and undergoes a faster SN2 reaction?

The secondary alkyl halide (option b) 2-bromobutane is chiral and undergoes a faster SN1 reaction. The chiral carbon atom is marked with an asterisk. A chiral carbon atom is a carbon atom with four different atoms or groups of atoms. The primary alkyl halide (option a) 1-bromobutane is achiral and undergoes a faster SN2 reaction. SN2 reaction gives inversion of configuration. SN1 reaction gives racemization.