Question

Match the organic compound column-I with the Lassaigne’s test results in column-II appropriately.

Column-I	Column-II
(A) aniline	(i) red color with $FeC{{l}_{3}}$
(B) Benzene sulfonic acid	(ii) violet color with sodium nitroprusside
(C) thiourea	(iii) blue color with and acidic solution of $FeS{{O}_{4}}$

(A) A-ii, B-iii, C-i
(B) A-iii, B-ii, C-i
(C) A-ii, B-i, C-iii
(D) A-iii, B-i, C-ii

Answer 1

. Unknown organic compound analysis and identification constitutes a very important part of organic chemistry as a qualitative analysis of organic compounds. Preliminary tests, physical constants, analysis of elements present, solubility tests, and group classification tests are general schemes of qualitative analysis of organic compounds.

Complete step by step answer:
Lassaigne’s test:
In a qualitative analysis of organic compounds, a test for the detection of nitrogen, sulfur, and halogens present in organic compounds is Lassaigne’s test. In this test, the organic compound and a small piece of Na metal are heated in a fusion tube. The basic principle of this test is that Na converts the elements in organic compound into ionic form
(A) Aniline with Lassaigne’s test: the aniline compound is boiled $FeS{{O}_{4}}$ with concentrated ${{H}_{2}}S{{O}_{4}}$ , which will appear on Prussian blue color indicates the presence of nitrogen in the given organic compound.

(B) benzene sulfonic acid with Lassaigne’s test: the given compound treated with sodium nitroprusside gives the appearance of violet color indicates the sulfur present in the benzene sulfonic acid.

(C) thiourea with Lassaigne’s test: this compound on reacting with $FeC{{l}_{3}}/FeS{{O}_{4}}$ will give blood-red color.
So, the correct answer is “Option B”.

Note: When an organic compound contains both nitrogen and sulfur, they combine during fusion heat from sodium thiocyanate in lassaigne’s test. This sodium thiocyanate is heated with ferrous sulfates which give blood-red color. This test is only for N but not carbon atoms.