Identify the compound in each of the following pairs that reacts with sodium iodide in acetone at the faster rate:
(a) 1-Bromopentane or 3-bromopentane
(b) 2-Chloropentane or 2-fluoropentane
(c) 2-Bromo-2-methylhexane or 2-bromo-5-methylhexane
(d) 2-Bromopropane or 1-bromodecane