Q.Classify carbohydrates into monosaccharides, oligosaccharides and polysaccharides, giving at least one named example of each.

Chitin is built from repeating N-acetyl-D-glucosamine monomers joined by beta-1,4 glycosidic linkages.

Chitin is a structural homopolysaccharide, chemically very similar in architecture to cellulose (which is a beta-1,4-linked chain of plain D-glucose units), but chitin's repeating monomer is instead N-acetyl-D-glucosamine — a glucose derivative in which the hydroxyl group at carbon-2 is replaced by an acetylated amino group (-NHCOCH3). This substitution allows chitin to form very strong hydrogen-bonded microfibrils, which is why it makes such a tough structural material (fungal cell walls, insect and crustacean exoskeletons). The other options are the monomers/hydrolytic components of different molecules entirely: alpha-1,4-glucan malto hydrolase is an enzyme (amylase-type), beta-D-glucose units make up cellulose/callose, and D-glucuronic acid is a component of some plant gums and mucilages, not chitin.

Cellulose is a homopolysaccharide of β-D-glucose units, and the glucose monomers are linked together specifically by β-(1→4) glycosidic bonds, giving it a straight, unbranched, highly hydrogen-bonded chain.

Cellulose is the chief structural polysaccharide of plant cell walls. It is built entirely of D-glucose units in the β-anomeric configuration, joined by glycosidic bonds between carbon-1 of one glucose unit and carbon-4 of the next — hence a β-(1→4) linkage.

This particular linkage forces alternate glucose units to be rotated 180° relative to their neighbours, which allows the long cellulose chains to lie flat and pack tightly side-by-side through extensive hydrogen bonding, forming rigid microfibrils. (This is different from starch and glycogen, whose glucose units are joined by α-(1→4) linkages, giving a helical, easily digestible chain.)

The other options do not describe cellulose's actual bonding: a plain "1→3" linkage and N-acetyl side chains/N-acetyl D-glucosamine describe other polysaccharides (e.g., chitin uses N-acetylglucosamine units, not plain glucose).

Lactose = galactose + glucose joined by a $\beta$-1,4-glycosidic bond.

Lactose is a disaccharide made of one unit of $\beta$-D-galactose and one unit of $\beta$-D-glucose. The two monosaccharides are joined through their C-1 (of galactose, $\beta$-configuration) and C-4 (of glucose) carbons, i.e. a $\beta$-1,4-glycosidic linkage — the same linkage type found in cellulose but between different sugar units.

Maltose is two $\alpha$-D-glucose units joined between C1 of one and C4 of the other.

Maltose is a disaccharide made of two $\alpha$-D-glucopyranose units linked through an $\alpha$-1,4-glycosidic bond — the anomeric (C1, $\alpha$-configured) carbon of one glucose unit is joined via an oxygen bridge to the C4 hydroxyl of the second glucose unit. This is obtained on partial hydrolysis of starch.

Concentrated sulphuric acid removes the elements of water from sucrose, charring it to carbon.

Concentrated sulphuric acid is a powerful dehydrating agent. On sugar (sucrose, $C_{12}H_{22}O_{11}$), it removes water (in the ratio corresponding to the empirical formula, effectively $H_2O$ units) from the sugar molecule, leaving behind a black, porous mass of elemental carbon and releasing heat and steam/gases in the process:

$C_{12}H_{22}O_{11} \xrightarrow{conc.\ H_2SO_4} 12C + 11H_2O$

Ribose's open-chain form has OH on C2/C3/C4 (secondary) and C5 (primary).

The open-chain structure of ribose (an aldopentose) is $CHO-CHOH-CHOH-CHOH-CH_2OH$ (C1 to C5).

• C1 bears the aldehyde group ($-CHO$), no $-OH$ here.
• C2, C3, C4 each bear a hydroxyl on a carbon attached to two other carbons — these are secondary hydroxyls (3 in total).
• C5 bears $-CH_2OH$, a hydroxyl on a terminal carbon attached to only one other carbon — this is a primary hydroxyl (1 in total).

So ribose has 1 primary and 3 secondary hydroxyl groups.