Question

Which sugar is called invert sugar? Why is it called so?

Answer 1

Sucrose is called invert sugar.
Sucrose is dextrorotatory but upon hydrolysis it gives dextrorotatory glucose and laevorotatory fructose. Since the laevorotation of fructose $(-{92.4}^{\circ })$ is more than dextrorotation of glucose $(+{52.5}^{\circ })$, the overall mixture is laevorotatory.

Thus, hydrolysis of sucrose brings about a change in the sign of optical rotation, from dextro $(+)$ to laevo $(-)$ and the product is named as invert sugar.