The incorrect statement from the…

Single correct+4 / -1Answer matches NTA’s final key

The incorrect statement from the following with respect to carbohydrates is:

All monosaccharides are reducing sugars.
The monosaccharide units obtained from hydrolysis of oligosaccharides are always the same.
Starch and cellulose are typical examples of polysaccharides, which are very high molecular weight compounds of more than ten monosaccharide units.
Open chain and cyclic structures co-exist at equilibrium that are responsible for certain properties as in the case of D-(+)-glucose.

Solution

A, correct. Every monosaccharide has a free aldehyde or ketone group (or a hemiacetal that opens to one), so all reduce Tollens' and Fehling's reagents.
B, incorrect. Oligosaccharides can be made of different units. Sucrose hydrolyses to glucose and fructose; lactose to glucose and galactose.
C, correct. Starch and cellulose are polymers of many glucose units.
D, correct. Glucose exists as an equilibrium of the cyclic α and β forms with a small amount of the open chain, which explains mutarotation and its reducing behaviour.

Answer: B.

Answer checked against the official answer key. The solution is our own working.