How many of the following are aldoses?
Glucose, D-Ribose, 2-Deoxy-D-ribose, Aldotriose, Ketotetrose, Ketopentose, Aldoheptose
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 5
A monosaccharide with an aldehyde group is an aldose; one with a keto group is a ketose. The name also carries the number of carbon atoms: an aldohexose is a six-carbon aldose, a ketopentose a five-carbon ketose.
Aldoses:
Glucose (an aldohexose)
D-Ribose (an aldopentose)
2-Deoxy-D-ribose (an aldopentose)
Aldotriose (a three-carbon aldose)
Aldoheptose (a seven-carbon aldose)
Not aldoses:
Ketotetrose — a four-carbon ketose.
Ketopentose — a five-carbon ketose.
Aldoses: glucose, D-ribose, 2-deoxy-D-ribose, aldotriose and aldoheptose = 5.
NCERT (2026-27 edition):
10.1.2 Monosaccharides – “Monosaccharides are further classified on the basis of number of carbon atoms and the functional group present in them. If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is known as a ketose. Number of carbon atoms constituting the monosaccharide is also introduced in the name as is evident from the examples given in Table 10.1”
Table 10.1: Different Types of Monosaccharides
| Carbon atoms | General term | Aldehyde | Ketone |
|---|---|---|---|
| 3 | Triose | Aldotriose | Ketotriose |
| 4 | Tetrose | Aldotetrose | Ketotetrose |
| 5 | Pentose | Aldopentose | Ketopentose |
| 6 | Hexose | Aldohexose | Ketohexose |
| 7 | Heptose | Aldoheptose | Ketoheptose |
10.1.2.1 Glucose – “Glucose is an aldohexose and is also known as dextrose.”
10.1.5 Importance of Carbohydrates – “Two aldopentoses viz. D-ribose and 2-deoxy-D-ribose … are present in nucleic acids.”