Q55 / 180 · COMEDK 2025 (25 May Shift) · Chemistry
Identify the incorrect statement
- AIn organic compounds resonance effect operates only in unsaturated compounds and results in delocalisation of electrons.
- BLarger the number of methyl groups linked to the doubly bonded Carbon atoms, greater is the stability of the alkene.
- Correct answerCThe Prussian blue precipitate formed during Lassaigne's test for detection of Nitrogen in an organic compound is due to formation of $\mathrm{Fe}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]_2 \times \mathrm{H}_2 \mathrm{O}$
- DIn the Carius method for estimation of halogens in an organic compound, the compound is heated with fuming nitric acid in presence of $\mathrm{AgNO}_3$.
Solution
(1) Correct: Resonance effect involves delocalization of $\pi$-electrons or lone pairs, requiring unsaturated or conjugated systems.
(2) Correct: More alkyl (methyl) groups on doubly bonded carbons increase stability via hyperconjugation.
(3) Incorrect: The correct formula for Prussian blue is $Fe_4[Fe(CN)_6]_3 \cdot xH_2O$. The formula given in option (3) has the wrong subscript (2 instead of 3) for the hexacyanoferrate ion.
(4) Correct: In the Carius method, the organic compound is heated with fuming nitric acid in presence of $AgNO_3$ to convert halogens into measurable silver halide precipitate.
The incorrect statement is (3).
(2) Correct: More alkyl (methyl) groups on doubly bonded carbons increase stability via hyperconjugation.
(3) Incorrect: The correct formula for Prussian blue is $Fe_4[Fe(CN)_6]_3 \cdot xH_2O$. The formula given in option (3) has the wrong subscript (2 instead of 3) for the hexacyanoferrate ion.
(4) Correct: In the Carius method, the organic compound is heated with fuming nitric acid in presence of $AgNO_3$ to convert halogens into measurable silver halide precipitate.
The incorrect statement is (3).
Hence, the correct answer is option: 'C'.