The enantiopure ketone shown (the stereocentre is fixed) is reduced with sodium borohydride, followed by work-up. What does the product mixture contain?

(R)-3-Methylpentan-2-one has one stereocentre. Reduction creates a second one at C-2, whose configuration may be either. Since the existing stereocentre is fixed, the two faces of the carbonyl are diastereotopic and attack is unequal. The product is a mixture of two diastereomers, each optically active, in unequal amounts.