on mercuration-demercuration produces the major product:

The reagent $$Hg(OAc)_2/H_2O$$ followed by $$NaBH_4$$ adds an $$-OH$$ group to the more substituted carbon of the alkene and an $$-H$$ to the less substituted carbon.

Unlike acid-catalyzed hydration, this process occurs via a cyclic mercurinium ion intermediate, which prevents carbocation rearrangement.

For allylbenzene, the more substituted carbon in the vinyl group is the secondary carbon ($$C_2$$).

The major product is therefore 1-phenylpropan-2-ol.