Question

a. how many stereocenters are present in this monosaccharide?

Explanation:

Step1: Recall stereocenter definition

A stereocenter is a carbon atom bonded to four different groups.

Step2: Identify carbon atoms in the monosaccharide

The monosaccharide has 3 carbon atoms. The top - most carbon is part of a carbonyl group ($C = O$) and is not a stereocenter as it has a double - bond. The bottom - most carbon has two hydrogen atoms and is not a stereocenter. The middle carbon has four different groups: $-OH$, $-H$, $-CH_2OH$ and the carbonyl - containing group.

Answer:

1