Which of the two is functional isomer? Glucose and lactose or xylose and galactose.

Explanation

To determine which pair of compounds are functional isomers, we need to analyze the structures and functional groups of the given compounds: glucose, lactose, xylose, and galactose.

### Step 1: Identify the Compounds
- **Glucose**: A simple sugar (monosaccharide) with the formula C₆H₁₂O₆.
- **Lactose**: A disaccharide composed of glucose and galactose, with the formula C₁₂H₂₂O₁₁.
- **Xylose**: A pentose sugar (monosaccharide) with the formula C₅H₁₀O₅.
- **Galactose**: A simple sugar (monosaccharide) with the formula C₆H₁₂O₆, similar to glucose but with a different arrangement of atoms.

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