Which carbohydrate is used in the silvering of mirrors?

Which of the following correctly represents $D$-glyceraldehyde?

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:

Which of the following is the sweetest sugar?

The number of possible stereoisomers for glucose is .......... .

Glucose has which functional group$(s)$?