Which of the following is a polysaccharide?

Dextrin

The correct answer is option 3. Dextrin.

Let us delve into each term and understand why only "Dextrin" is a polysaccharide:

1. Gentiobiose: Gentiobiose is a disaccharide, which means it consists of two monosaccharide units linked together. In the case of gentiobiose, these two units are glucose molecules linked by a glycosidic bond. While gentiobiose is a carbohydrate, it is not a polysaccharide because it only contains two sugar units.

2. Fructose: Fructose is a monosaccharide, which means it is the simplest form of carbohydrate and cannot be broken down into smaller sugar units. It is commonly found in fruits and honey. Since fructose consists of only one sugar unit, it is not considered a polysaccharide.

3. Dextrin: Dextrin, on the other hand, is a polysaccharide. It is formed by the partial hydrolysis of starch, which is itself a polysaccharide composed of many glucose units linked together. When starch is partially broken down by enzymes or heat, it produces dextrins, which are shorter chains of glucose molecules. Dextrins can have various sizes and structures depending on the extent of starch hydrolysis.

So, among the options provided, only Dextrin qualifies as a polysaccharide.