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JEE Main 2025 Jan 28 Shift 1, Chemistry Q20: Carbohydrates

JEE Main2025Jan 28, Shift 1Chemistry
Q.

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°C and 2-3 atmosphere pressure produces glucose.

In the light of the above statements, choose the correct answer from the options given below

  1. A

    Both Statement I and Statement II are false

  2. B

    Statement I is false but Statement II is true

  3. C

    Statement I is true but Statement II is false

  4. D

    Both Statement I and Statement II are true

Solution

Statement I: In glucose pentaacetate, all five hydroxyl groups (including the anomeric -OH) are acetylated, locking the molecule in the cyclic acetal-like form. The free aldehyde group is no longer accessible, so it cannot condense with 2,4-DNP. Statement I is false.

Statement II: Starch hydrolyses to glucose under hot dilute mineral acid; on an industrial scale, treatment with HSO at 100°C and 2-3 atm does give glucose. Statement II is true.

Statement I is false and Statement II is true, option (2).

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