In the process of forming 'mercerised cellulose',the swelling of cellulose is caused by

Which carbon atom of glucose,numbered from $C-1$ to $C-6$,converts its functional group to a $-COOH$ group when heated with $Br_2$ water?

Glucose on prolonged heating with $HI$ gives product $P$. The product $P$ is

$C_2$-epimer of $D$-Glucose is

For 'invert sugar',the correct statement$(s)$ is(are)
(Given: specific rotations of $(+)$-sucrose,$(+)$-maltose,$L-(-)$-glucose and $(+)$-fructose in aqueous solution are $+66^{\circ}, +140^{\circ}, -52^{\circ}$ and $+92^{\circ}$,respectively)
$(A)$ 'invert sugar' is prepared by acid catalyzed hydrolysis of maltose
$(B)$ 'invert sugar' is an equimolar mixture of $D-(+)$-glucose and $D-(-)$-fructose
$(C)$ specific rotation of 'invert sugar' is $-20^{\circ}$
$(D)$ on reaction with $Br_2$ water,'invert sugar' forms saccharic acid as one of the products

What is the molecular formula of glyceraldehyde?