How many optical isomers does glucose have?

The number of chiral carbons present in sucrose is

Which of the following is $NOT$ correct about fructose?

The letters $'D'$ or $'L'$ before the name of a stereoisomer of a compound indicate the correlation of configuration of that particular stereoisomer. This refers to their relation with one of the isomers of glyceraldehyde. Predict whether the following compound has $'D'$ or $'L'$ configuration.

The formulas of $A$ and $B$ for the following reaction sequence are:

Which of the following is present in $RNA$ only?