Question 9

Analyze each option: (A) Both glucose and gluconic acid are oxidized by concentrated $HNO_3$ to saccharic acid (a dicarboxylic acid). The reagent oxidizes both the aldehyde/hemicetal group and the primary alcohol group. So, the statement is false. (B) Fructose is a ketohexose and usually does not reduce Fehling's solution. however, in the presence of basic reagents like Fehling's solution, it undergoes Lobry de Bruyn-van Ekenstein rearrangement to form glucose and mannose (another aldohexose), which then give a positive test. This is correct. (C) Invert sugar is indeed the equimolar mixture of $D$-glucose and $D$-fructose obtained by the hydrolysis of sucrose (a disaccharide). This is correct. (D) Using the standard values for $D$-isomers: Specific rotation of $D$-glucose is $+52.5^{\circ}$ and $D$-fructose is $-92.5^{\circ}$. For an equimolar mixture, the specific rotation is the average: $\frac{+52.5^{\circ} + (-92.5^{\circ})}{2} = -20^{\circ}$. The value $-40^{\circ}$ is incorrect.