The option (4) is incorrect as sucrose does not contain free -CHO group to react with phenylhydrazine.
All the other options are correct.

On hydrolysis with dilute acid, sucrose produces glucose and fructose.

Since glucose shows reducing property, the hydrolysis product reduces Fehling's solution.
Sucrose is dextrorotatory with specific rotation of +66.50. On hydrolysis, it produces D (+) glucose and D (–) fructose. Since D (–) fructose has greater specific rotation than D (+) glucose, the resulting mixture is laevorotatory.

α-D glucose and β-D glucose are the isomers which differ in the orientation (configuration) of H and OH groups around C1 atom.

Glucose reacts with three molecules of phenylhydrazine to form glucosazone, a yellow solid. So, (2) is correct.

Glucose reduces Fehling`s solution to give salt of gluconic acid and red precipitates of cuprous oxide.
So, (1) is wrong.
Glucose fails to respond to some reactions of aldehydes. It cannot form a bisulphate compound indicating that glucose presumably contains a potential aldehyde group but in very low concentration. So, (3) is wrong.
When glucose is reacted with excess of acetic anhydride, glucose penta-acetate is formed indicating the presence of five hydroxyl groups. So, (4) is wrong.

The carbon atom which becomes asymmetric when the straight chain form of a monosaccharide changes into the ring form is known as anomeric carbon atom. Anomers are special epimers.

The folding of the polypeptide chain is stabilised by weak non covalent interactions.

This option is correct because if three amino acids are combined, there will be two peptide linkages between them, and the product will be tripeptide because it is made up of three amino acids.

Formula of "A" = C : H : O = 42.1/12 : 6.4/1 : 51.5/16 = 3.51 : 6.4 : 3.22 = 11.99 : 21.89 : 11 = 12 : 22 : 11
So, "A" is C₁₂H₂₂O₁₁.

All the alternatives have the same molecular formula. Sucrose does not have reducing property. So, "A" is sucrose and option (3) is correct.

On hydrolysis with dil. HCl, a mixture of "B" (glucose) and "C" (fructose) is formed. Glucose reduces Fehling's solution and produces a yellow crystalline compound (osazone) with excess phenylhydrazine. Fructose does not reduce Fehling's solution but produces the same osazone with excess phenylhydrazine.

Formula of B = C : H : O = 40/12 : 6.67/1 : 53.33/16 = 3.33 : 6.67 : 3.33 = 1 : 2 : 1
So, empirical formula = CH₂O
Molecular formula = (CH₂O)_n
All the alternatives given have the formula = (CH₂O)₆ = C₆H₁₂O₆.
Glucose has reducing properties and can be obtained by the hydrolysis of cane sugar.

Due to resonance, C-N bond in protein acquires a double bond character and is smaller than its usual double bond length.