Step 1: Understanding the Concept:
Inversion refers to the change in the sign of optical rotation during the hydrolysis of sucrose.
Step 2: Detailed Explanation:
Sucrose is dextrorotatory (\( +66.5^\circ \)).
Upon hydrolysis, it yields an equimolar mixture of D-(+)-glucose (\( +52.5^\circ \)) and D-(-)-fructose (\( -92.4^\circ \)).
Since the levorotation of fructose is greater than the dextrorotation of glucose, the overall mixture becomes levorotatory (\( -39.9^\circ \)).
This mixture is called invert sugar.
Step 3: Final Answer:
Invert sugar is the levorotatory mixture of glucose and fructose obtained from the hydrolysis of dextrorotatory sucrose.