Reduction of `D`-glucose forms `D`-sorbitol while that of `D`-fructose forms a mixture of `D`-sorbitol and `D`-mannitol.

Relation between D-Glucose & D-Fructose is

A compound (C_(6)H_(12)O_(6)) on reaction with phenyl-hydrazine gives a yellow ppt. and with Na produces a mixture of sorbitol and mannitol. The compound is-

When an aqueous solution of D-glucose is treated with a base, it is converted into D-fructose and D-mannose, this conversion (isomerisation) involves