Given below are two statements :
Statement I: D-(+)-glucose + D-(+)-fructose $$\xrightarrow{-H_2O}$$ sucrose
sucrose $$\xrightarrow{Hydrolysis}$$ D-(+)-glucose + D-(+)-fructose
Statement II : Invert sugar is formed during sucrose hydrolysis.
In the light of the above statements, choose the correct answer from the options given below-

For any carbohydrate we must distinguish two separate ideas:
  • the D/L configuration (decided by the Fischer projection)
  • the sign of optical rotation, given by ( + ) for dextrorotation and ( - ) for levorotation.
A molecule can be D and still rotate the plane of light to the left; the sign is completely independent of the D/L prefix.

Checking Statement I

The condensation that produces sucrose involves one molecule of $$\alpha$$-D-(+)-glucopyranose and one molecule of $$\beta$$-D-(-)-fructofuranose:

$$\alpha\text{-D-(+)-glucose}\;+\;\beta\text{-D-(-)-fructose}\; \xrightarrow{-H_2O}\;\text{sucrose}$$

Therefore the correct second reactant is D-(-)-fructose, not D-(+)-fructose. Because Statement I writes D-(+)-fructose, it gives the wrong optical sign and is false.

Checking Statement II

Sucrose has a specific rotation of $$+66.5^{\circ}$$. On hydrolysis it yields one molecule each of D-(+)-glucose ($$+52.5^{\circ}$$) and D-(-)-fructose ($$-92.0^{\circ}$$). The resulting mixture has an overall rotation

$$\frac{(+52.5)+(-92.0)}{2}= -19.75^{\circ}\;(\text{approximately }-20^{\circ})$$

Thus the sign of rotation changes from positive to negative; this change is called inversion and the product mixture is known as invert sugar. Hence Statement II is true.

Conclusion

Statement I is false, while Statement II is true. Therefore the correct option is Option B.