An unknown disaccharide 'X' does not exhibit mutarotation and fails to form an osazone derivative. Upon acidic hydrolysis, it yields a mixture that is levorotatory. Identify the disaccharide 'X'.

Step-by-step solution

The inability of disaccharide 'X' to exhibit mutarotation and form an osazone derivative indicates the absence of a free hemiacetal group. Thus, 'X' is a non-reducing sugar. Among the given options, maltose, lactose, and cellobiose are reducing sugars as they have a free anomeric carbon. Sucrose is a non-reducing sugar because its glycosidic linkage involves the anomeric carbons of both glucose ( C₁ ) and fructose ( C₂ ). Furthermore, sucrose is dextrorotatory, but upon acidic hydrolysis, it yields a mixture of D-g