Monosaccharides are carbohydrates which cannot be hydrolyzed to simple molecules. They may contain 3-7 carbon atoms but monosaccharides containing five and six carbon atoms are more abundant in nature. Those containing an aldehyde group are called aldoses while those containing a keto group are called ketoses. The aldehyde group is always present at C₁ while the keto group is usually present at C₂.  All monosaccharides reduce Tollens reagent as well as Fehling's solution and hence are called reducing sugars. Pentoses ands hexoses have cyclic structures, furanose (five membered) and pyranose (six membered). Ribose in RNA and fructose in sucrose exist in the furanose form while glucose, mannose, galactose, etc. all exist in the pyranose form. During ring formation C₁ in aldohexoses and C₂ in fructose becomes chiral and hence all these monosaccharides exist in two stereoisomeric forms called the  α-anomer and the β-anomer while C₁ and C₂ are called glycosidic or anomeric carbon atoms and the bonds connected to glycosidic carbon are called glycosidic linkages. In contrast, stereoisomers, which differ in configuration at any other chiral carbon are called epimers. When two molecule of the same or different monosaccharide combine together through glycosidic linkage, a disaccharide is formed. All monosaccharides and reducing disaccharides react with excess of phenyl hydrazine to form osazones which are oftenly used for their characterization. 

In polysaccharides, the linkage connecting monosaccharide units are called 

Glycoside linkages 

The correct answer is option 1. Glycoside linkages.

A glycosidic linkage (or glycosidic bond) is a type of covalent bond that connects two monosaccharide units in a carbohydrate. This bond forms between the anomeric carbon of one sugar and the hydroxyl group of another sugar.

Formation of Glycosidic Linkages

Formation Reaction: The formation of a glycosidic linkage occurs through a dehydration (or condensation) reaction. This involves the elimination of a water molecule when the hydroxyl group (-OH) of one monosaccharide reacts with the anomeric carbon of another monosaccharide.

Example: In the formation of sucrose, the hydroxyl group of glucose reacts with the anomeric carbon of fructose, releasing water and forming a glycosidic bond.

Types of Glycosidic Linkages:

α-Glycosidic Linkages: These occur when the hydroxyl group on the anomeric carbon is below the plane of the sugar ring. For example, in starch and glycogen, the glucose units are connected by α-1,4 and α-1,6-glycosidic linkages.

β-Glycosidic Linkages: These occur when the hydroxyl group on the anomeric carbon is above the plane of the sugar ring. For example, in cellulose, glucose units are connected by β-1,4-glycosidic linkages.

Role in Polysaccharides

Polysaccharides are long chains of monosaccharide units linked by glycosidic bonds. They can be linear or branched. Examples include starch (a storage form of glucose in plants), glycogen (a storage form of glucose in animals), and cellulose (a structural component in plant cell walls).

Examples of Polysaccharides:

Starch: Composed of glucose units linked by α-1,4 and α-1,6-glycosidic bonds. It is a major storage form of energy in plants.

Glycogen: Similar to starch but more highly branched, it serves as a storage form of glucose in animals.

Cellulose: Composed of glucose units linked by β-1,4-glycosidic bonds, it provides structural support in plant cell walls.

Other Terms

2. Nucleoside Linkage: Refers to the bond between a sugar and a nitrogenous base in nucleotides of nucleic acids (DNA and RNA).

3. Glycogen Linkage: Not a standard term; glycogen is a polysaccharide made up of glycosidic linkages.

4. Peptide Linkage: The bond between amino acids in proteins, known as a peptide bond.

Conclusion

In summary, glycosidic linkages are crucial for forming polysaccharides by connecting monosaccharide units through dehydration reactions. They determine the structure and function of carbohydrates in biological systems. So the term that correctly describes the bond connecting monosaccharide units in polysaccharides is: Glycoside linkages.