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MCQEasyJEE 2026Detection of Functional Groups

JEE Chemistry 2026 Question with Solution

Given below are two statements:

Statement I: Griess–Ilosvay test is used for the detection of nitrite ion, which involves the use of sulphanilic acid and α\alpha-naphthylamine reagent.

Statement II: In the above test, sulphanilic acid is diazotized by the acidified nitrite ion, which on further coupling with α\alpha-naphthylamine forms an azo-dye.

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

  • A

    Statement I is false but Statement II is true

  • B

    Both Statement I and Statement II are true

  • C

    Both Statement I and Statement II are false

  • D

    Statement I is true but Statement II is false

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Two statements about the Griess–Ilosvay test for detection of nitrite ion.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Concept: The Griess–Ilosvay test is a qualitative test for nitrite, based on diazotization followed by azo-coupling to give a colored azo dye.

Step 1: Check Statement I. Sulphanilic acid reacts with nitrite ions in acidic medium, and α\alpha-naphthylamine is used as the coupling reagent. Therefore, the test does involve both reagents for the detection of nitrite ions.

⇒Statement I is true\Rightarrow \text{Statement I is true}

Step 2: Check Statement II. In acidic medium, nitrite ion produces nitrous acid. This diazotizes sulphanilic acid to form a diazonium salt, which then couples with α\alpha-naphthylamine to form a red or pink azo dye.

⇒Statement II is also true\Rightarrow \text{Statement II is also true}

Step 3: Conclude. Since both statements are correct, the correct option is B.

Therefore, both Statement I and Statement II are true.

Common mistakes

  • Assuming the test detects nitrate ion instead of nitrite ion. This is wrong because the Griess–Ilosvay test is specific for nitrite through diazotization chemistry. Check the ion mentioned in the statement carefully before evaluating it.

  • Confusing the role of sulphanilic acid and α\alpha-naphthylamine. Sulphanilic acid is first diazotized, while α\alpha-naphthylamine acts as the coupling reagent. Do not interchange their functions in the reaction sequence.

  • Thinking that statement-explanation questions require Statement II to explain Statement I in order for both to be true. Here the options ask only the truth values of the two statements. First determine whether each statement is true or false independently.

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