The halide shown is converted to its Grignard reagent with magnesium in dry ether; (R)-2-methyloxirane is added, followed by $\mathrm{H}{}_3\mathrm{O}{}^{+}$. Which structure is the product?

A Grignard reagent opens an epoxide at the less hindered ring carbon (SN2-like), here the CH2 carbon. The stereocentre (the CH(CH3) carbon) is not attacked, so its spatial arrangement is retained, giving 1-phenylpropan-2-ol with the same geometry (the label stays R; RDKit confirms). Attack at the CH carbon would give 2-phenylpropan-1-ol, and the enantiomeric alcohol would need inversion at the stereocentre.