The correct order of reactivity of the following alcohols with hydrobromic acid is 1-phenylpropan-1-ol \(\underset{(\mathrm{II})}{\text { 1-phenylpropan-2-ol }}{\text { 3-phenylpropan-l-ol }}{(\mathrm{III})}\) (a) \(\mathrm{I}>\mathrm{II}>\mathrm{III}\) (b) \(\mathrm{I}>\mathrm{III}>\mathrm{II}\) (c) \(\mathrm{III}>\mathrm{I}>\mathrm{II}\) (d) \(\mathrm{III}>\mathrm{II}>\mathrm{I}\)

The given reaction is an acid-catalyzed substitution reaction where hydrobromic acid (HBr) reacts with the alcohols. In this type of reaction, the oxygen atom in the alcohol donates a lone pair of electrons to form a bond with a proton from HBr. This results in a protonated alcohol, which undergoes a nucleophilic substitution reaction with the bromide ion (Br-) to form an alkyl bromide product.

To determine the reactivity of each alcohol, we need to examine their structures: (I) 1-phenylpropan-1-ol: There is no steric hindrance at the alcohol site, and the phenyl group is connected to the carbon atom next to the alcohol site. The oxygen in the alcohol site does not participate in resonance with the benzene ring in the phenyl group. (II) 1-phenylpropan-2-ol: There is a moderate amount of steric hindrance at the alcohol site, and the phenyl group is connected to the carbon atom two positions away from the alcohol site. The oxygen in the alcohol site can participate in resonance with the benzene ring in the phenyl group through the alkene-like intermediate formed during the reaction. (III) 3-phenylpropan-1-ol: There is no steric hindrance at the alcohol site, and the phenyl group is connected to the carbon atom three positions away from the alcohol site. The oxygen in the alcohol site does not participate in resonance with the benzene ring in the phenyl group.

Now that we have looked at the structure of each alcohol, we can assess their reactivity with HBr based on steric hindrance and resonance stabilization: 1. Steric hindrance: In general, greater steric hindrance decreases the reactivity of alcohols with HBr. Therefore, (II) would be the least reactive alcohol among the three due to steric hindrance at the alcohol site. 2. Resonance stabilization: Alcohols that have their oxygen atom participating in resonance with the phenyl ring (benzene ring) are more stable and, thus, less reactive. The only alcohol in this case with resonance stabilization is (II). Taking both factors into account, the correct order of reactivity should be (III) > (I) > (II), as (III) and (I) have no steric hindrance and no resonance stabilization, while (II) has a moderate amount of steric hindrance and is resonance stabilized. Therefore, the correct answer is (c) \(\mathrm{III}>\mathrm{I}>\mathrm{II}\).