Select the correct statement among the following:

Cellulose upon acetylation with excess acetic anhydride $/$ $H_2SO_4$ (catalytic) gives cellulose triacetate whose structure is

Given below are two statements: one is labelled as Assertion $A$ and other is labelled as Reason $R.$
Assertion $A :$ Sucrose is a disaccharide and a non-reducing sugar.
Reason $R :$ Sucrose involves glycosidic linkage between $C_{1}$ of $\beta$-glucose and $C_{2}$ of $\alpha$-fructose.
Choose the most appropriate answer from the options given below :

What are the pairs of stereoisomers that differ in configuration at only one carbon atom called?

If $\alpha-D-(+)$-glucose is dissolved in water and kept for a few hours,the major constituent$(s)$ present in the solution is (are)

Number of optical isomers in the open chain structure of glucose is