Name the sugar present in milk. How many monosaccharide units are present in it? What are such oligosaccharides called?

(N/A) The sugar present in milk is lactose.
Lactose is a disaccharide composed of $D$-Galactose and $D$-Glucose units linked by a $\beta-C_1-O-C_4$ glycosidic linkage.
It contains $2$ monosaccharide units.
Oligosaccharides that yield $2$ monosaccharide units upon hydrolysis are called disaccharides.