Aldopentoses named as ribose and $2-$deoxyribose are found in nucleic acids. What is their relative configuration?

Compound $A$,$C_5H_{10}O_5$,gives a tetraacetate with $Ac_2O$ and oxidation of $A$ with $Br_2-H_2O$ gives an acid,$C_5H_{10}O_6$. Reduction of $A$ with $HI$ gives isopentane. The possible structure of $A$ is:

$L$-isomer of a compound $A$ $(C_{4}H_{8}O_{4})$ gives a positive test with $[Ag(NH_{3})_{2}]^{+}$. Treatment of $A$ with acetic anhydride yields a triacetate derivative. Compound $A$ produces an optically active compound $B$ and an optically inactive compound $C$ on treatment with bromine water and $HNO_{3}$ respectively. Compound $A$ is ....

$A$ polysaccharide '$X$' on boiling with dil $H_2SO_4$ at $393 \ K$ under $2-3 \ atm$ pressure yields '$Y$'. '$Y$' on treatment with bromine water gives gluconic acid. '$X$' contains $\beta-$glycosidic linkages only. Compound '$X$' is ..... .

The number of chiral carbon atoms present in the open-chain structure of $D-(-)$-fructose is:

Which of the following is a non-reducing sugar?