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Biomolecules question

2025 · 28 Jan · Shift 1 · Q3
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Biomolecules question

2025 · 28 Jan · Shift 1 · Q3

JEE MainChemistryBiomoleculesMCQ+4 / −1
Given below are two statements: Statement I : D-glucose pentaacetate reacts with 2,4 -dinitrophenylhydrazine Statement II : Starch, on heating with concentrated sulfuric acid at 100∘C100^{\circ} \mathrm{C}100∘C and 2−3atmosphere2-3 \mathrm{atmosphere}2−3atmosphere pressure produces glucose. In the light of the above statements, choose the correct answer from the options given below
  1. A
    Statement I is true but Statement II is false
  2. B
    Both Statement I and Statement II are true
  3. C
    Statement I is false but Statement II is true
  4. D
    Both Statement I and Statement II are false
View written solutionFree

Correct answer: C

  1. Analyze Statement I

    Statement I: D-glucose pentaacetate reacts with 2,4-dinitrophenylhydrazine (DNPH).

    • DNPH reacts with free carbonyl groups such as aldehydes and ketones.
    • In D-glucose pentaacetate, all the hydroxyl groups including the anomeric hydroxyl are acetylated.
    • Therefore, the molecule is locked in its acetal form and does not have a free aldehyde group available.
    • Hence, it does not react with DNPH.

    So, Statement I is false.

  2. Analyze Statement II

    Statement II: Starch, on heating with concentrated sulfuric acid at 100∘C100^\circ \mathrm{C}100∘C and 222-333 atmospheres pressure produces glucose.

    • Starch is a polysaccharide made up of many units of α\alphaα-D-glucose.
    • On hydrolysis in acidic medium, starch breaks down ultimately into glucose.
    • Thus, the statement that starch under such conditions produces glucose is true in essence.

    So, Statement II is true.

  3. Choose the correct option

    • Statement I: False
    • Statement II: True

    Therefore, the correct option is:

    C: Statement I is false but Statement II is true\boxed{\text{C: Statement I is false but Statement II is true}}C: Statement I is false but Statement II is true​

  4. Comparison with stored correct answer

    • Derived answer: C
    • Stored correct answer: C

    They match.

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