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D-ribose and D-mannose are both pentose monosaccharides, meaning they have five carbon atoms in their structure. The Fischer projection representations for D-ribose and D-mannose are depicted below, with carbon atoms numbered 1 to 5 from top to bottom. D-ribose: HOCH2-(1) | C----OH (2) | OH--C (3) | C----OH (4) | CH2OH (5) D-mannose: HOCH2-(1) | C----OH (2) | OH--C (3) | C----OH (4) | C (5) | CH2OH

Review the structure of D-ribose to determine which carbon atoms meet the criterion for being chiral (four different groups attached). Carbon atom 2: Four different groups are attached (OH, H, HO-C, and HOCH2). Carbon 2 is chiral. Carbon atom 3: Four different groups are attached (OH, H, HO-C, and C-OH). Carbon 3 is chiral. Carbon atom 4: Four different groups are attached (OH, H, C-OH, and CH2OH). Carbon 4 is chiral. Carbon atom 5: Only three different groups are attached (HO-C, H, and H). Carbon 5 is not chiral. Chiral carbon atoms in D-ribose are C2, C3, and C4.

Review the structure of D-mannose to determine which carbon atoms meet the criterion for being chiral (four different groups attached). Carbon atom 2: Four different groups are attached (OH, H, HO-C, and HOCH2). Carbon 2 is chiral. Carbon atom 3: Four different groups are attached (OH, H, HO-C, and C-OH). Carbon 3 is chiral. Carbon atom 4: Four different groups are attached (OH, H, C-OH, and CH2OH). Carbon 4 is chiral. Carbon atom 5: Only three different groups are attached (HO-C, H, and H). Carbon 5 is not chiral. Chiral carbon atoms in D-mannose are C2, C3, and C4. After completing these steps, we can conclude that the chiral carbon atoms found in the monosaccharides D-ribose and D-mannose are C2, C3, and C4.