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Answer the following… (Class 12 Chemistry SQP 2025-26, Q32A)

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ChemistryCBSE Class 12 · Sample paper, session 2025-26 · 5 marks · Long answer

CBSE Class 12 Chemistry sample paper 2025-26: question 32(A)

From the official CBSE sample question paper for 2025-26, section E, question 32(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(A) · 5 marks · Long answerBiomolecules

Answer the following questions:
I. Identify and give any one point of difference between the protein present in the hair and protein present in egg albumin.
II. Both glucose and sucrose have aldehydic group, then why does only glucose reduces Fehling's Reagent and not sucrose?
III. Why do amino acids behave as salts?
IV. What chemical change takes place during curdling of milk?
V. Doctor advised a 50 year old woman enough exposure to sunlight and addition of fish and egg yolk to her diet. What is the possible disease diagnosed by the doctor?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

Open one hint at a time and try again before the next.

Hint 1

Classify proteins by shape, fibrous or globular, and think about solubility.

Hint 2

In sucrose, check which carbons of glucose and fructose form the glycosidic bond.

Hint 3

Sunlight, fish and egg yolk all supply the same vitamin, so which bone disease does its lack cause in adults?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. I. Hair contains keratin, a fibrous protein; egg albumin is a globular protein. Fibrous proteins have long, thread-like parallel chains held by H-bonds and disulphide bonds and are insoluble in water. Globular proteins are folded into spherical shapes and are generally soluble in water.

    1 mark

  2. II. In glucose the aldehydic group is free (open chain in equilibrium with the cyclic hemiacetal), so it reduces Fehling's solution. In sucrose, C1 of α-glucose is joined to C2 of β-fructose by a glycosidic bond, so both reducing groups are used up. No free –CHO (or >C=O) is left, so sucrose is a non-reducing sugar.

    1 mark

  3. III. An α-amino acid has both an acidic –COOH group and a basic –NH group. The proton moves from –COOH to –NH, forming a dipolar ion (zwitterion), H–CHR–COO. Because of this ionic nature, amino acids have high melting points and are water-soluble, like salts.

    1 mark

  4. IV. Bacteria (e.g. Lactobacillus) ferment the lactose in milk into lactic acid. The acid lowers the pH, which denatures and coagulates the milk protein (casein), forming curd.

    1 mark

  5. V. Sunlight, fish and egg yolk are sources of Vitamin D, so the woman has Vitamin D deficiency. The likely disease is osteomalacia/osteoporosis (soft, weak bones) in adults.

    1 mark

Answer: I. Keratin (fibrous, insoluble) vs albumin (globular, soluble). II. Sucrose has no free aldehyde group (glycosidic linkage involves C1 of glucose and C2 of fructose). III. Zwitterion formation. IV. Lactose → lactic acid, which coagulates casein. V. Vitamin D deficiency: osteomalacia/osteoporosis.

Where the marks are

  • Identifies fibrous (hair) vs globular (egg albumin) protein with one difference (1 mark)
  • No free aldehyde group in sucrose due to glycosidic linkage (1 mark)
  • Zwitterion formation from acidic and basic groups (1 mark)
  • Lactose converted to lactic acid by bacteria (1 mark)
  • Vitamin D deficiency disease: osteoporosis/osteomalacia (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biomolecules, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2025-26: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.