Hi Candidate,

SN 1 stands for First degree substitution reaction which obeys the stability of carbonation where the rate of reaction is in the order- Third degree is more than Second degree and it is more than First degree.

Tert- butyl bromide is a three degree compound where as N- Butyl bromide is a One degree compound, so it means that T-Butyl butyl bromide is more reactive towards SN 1 Reaction.

Hope that you have got your answer.