What is obtained when sucrose is heated with concentrated $H_2SO_4$?

Cellulose is a polymer of

Among the following,the incorrect statement is

Glucose and mannose are

Which carbon atom of glucose, numbered from $1$ to $6$, forms a hemiacetal structure by reacting with the $-CHO$ group to close the ring?

On prolonged heating with $HI$,glucose gives a compound '$C$',which can be obtained by Wurtz reaction using sodium metal and compound '$D$'. Identify '$D$'.