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MCQEasyJEE 2023Carbohydrates (Glucose, Fructose, Sucrose…)

JEE Chemistry 2023 Question with Solution

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Ketoses give Seliwanoff's test faster than Aldoses.

Reason (R): Ketoses undergo β\beta-elimination followed by formation of furfural.

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

  • A

    (A) is false but (R) is true

  • B

    Both (A) and (R) are true and (R) is the correct explanation of (A)

  • C

    (A) is true but (R) is false

  • D

    Both (A) and (R) are true but (R) is not the correct explanation of (A)

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given:

  • Assertion (A): Ketoses give Seliwanoff's test faster than Aldoses.
  • Reason (R): Ketoses undergo β\beta-elimination followed by formation of furfural.

Find: Determine which option correctly describes the truth value of Assertion and Reason.

Seliwanoff's test distinguishes ketoses from aldoses based on the faster dehydration of ketoses in the presence of resorcinol and concentrated hydrochloric acid.

Ketoses react faster and produce a deep red color more quickly than aldoses. Therefore, Assertion (A) is true.

Now examine the Reason. The explanation given is not correct. In Seliwanoff's test, the important process is dehydration leading to formation of furfural derivatives, specifically hydroxymethylfurfural for hexoses, not a simple β\beta-elimination followed by formation of furfural as stated.

Therefore, Reason (R) is false.

Hence, the correct conclusion is: (A) is true but (R) is false.

The correct option is C.

Common mistakes

  • Assuming that any statement mentioning furfural must be correct. This is wrong because Seliwanoff's test involves dehydration to furfural derivatives, especially hydroxymethylfurfural for hexoses. Focus on the exact mechanism stated, not only on the product name.

  • Confusing the basis of Seliwanoff's test with a general elimination reaction. This is incorrect because the distinguishing factor is the faster dehydration of ketoses in acidic medium. Identify the test principle before judging the Reason.

  • Treating Assertion-Reason questions as if both statements only need to sound related. This is wrong because the Reason must be factually correct and must explain the Assertion. First test each statement separately, then check the explanatory link.

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