When sugar \( X \) is boiled with dilute \( \mathrm{H_2SO_4} \) in alcoholic solution, two isomers \( A \) and \( B \) are formed. \( A \) on oxidation with \( \mathrm{HNO_3} \) yields saccharic acid where as \( B \) is laevorotatory. The compound \( X \) is: