Which of the following monosaccharides is a pentose ?

Options

A. Cellulose
B. Fructose
C. Ribose
D. Galactose

Answer

To determine which of the following monosaccharides is a pentose, we need to first understand what a pentose is. A pentose is a monosaccharide that contains five carbon atoms.

Let's analyze the options provided:

1. **Cellulose**: This is not a monosaccharide; it is a polysaccharide made up of many glucose units. Therefore, it cannot be a pentose.

2. **Fructose**: The molecular formula for fructose is C6H12O6. Since it has six carbon atoms, it is classified as a hexose, not a pentose.

3. **Ribose**: The molecular formula for ribose is C5H10O5. This indicates that it has five carbon atoms, which qualifies it as a pentose.

4. **Galactose**: Similar to fructose, the molecular formula for galactose is also C6H12O6. Thus, it is also a hexose and not a pentose.

Based on this analysis, the only monosaccharide listed that is a pentose is **ribose**.

### Final Answer:
The monosaccharide that is a pentose is **ribose**.