A polysaccharide 'X' on boiling with dil \( \mathrm{H_2SO_4} \) at \( 393 \, \text{K} \) under \( 2\text{-}3 \, \text{atm} \) pressure yields 'Y'. 'Y' on treatment with bromine water gives gluconic acid. 'X' contains \( \beta \)-glycosidic linkages only. Compound 'X' is:
