In the Kiliani-Fischer synthesis for the conversion of an aldose into its next higher homologue, the reagent employed in the first step is:

Step-by-step solution

The Kiliani-Fischer synthesis is a method used to increase the carbon chain length of an aldose by one carbon atom. In the first step of this synthesis, the aldose is treated with hydrogen cyanide ( HCN ). The nucleophilic addition of cyanide ion to the carbonyl group of the aldose forms a mixture of two epimeric cyanohydrins. These cyanohydrins are subsequently hydrolyzed to aldonic acids (or their lactones) and then reduced to yield the higher homologous aldoses. Therefore, the reagent employed in the first step