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MCQMediumJEE 2023Detection of Functional Groups

JEE Chemistry 2023 Question with Solution

Which of the following compounds would give the following set of qualitative analysis?

  • A

    (i) Fehling’s Test: Positive

    Five-membered aromatic ring containing two nitrogen atoms, with an aldehyde group directly attached to the ring on the right side.
  • B
    Five-membered aromatic ring containing two nitrogen atoms and one oxygen atom, with an aldehyde group directly attached to the ring on the right side.
  • C
    Five-membered aromatic ring containing two nitrogen atoms and one sulfur atom, with an aldehyde group directly attached to the ring on the right side.
  • D
    Five-membered aromatic ring containing nitrogen and sulfur, attached through a side chain to an aldehyde group on the right end.

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: The compound must give a positive Fehling’s test and also satisfy the condition for blood red colour with sodium nitroprusside.

Find: Which option matches both qualitative tests.

Aromatic aldehydes do not give Fehling’s test. Also, both nitrogen and sulfur must be present to obtain the blood red colour with sodium nitroprusside.

Therefore, the compound in option (4) satisfies the qualitative analysis. The solution text concludes that the compound in option (4) is correct, although the solution incorrectly states A. Hence, the defensible correct option is D.

Common mistakes

  • Choosing an aromatic aldehyde directly attached to the ring. This is wrong because aromatic aldehydes generally do not give Fehling’s test. Instead, eliminate options where the aldehyde is directly aromatic.

  • Ignoring the need for both nitrogen and sulfur in the sodium nitroprusside test. This is wrong because the blood red colour requires both elements. Instead, identify the option containing both N and S.

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