A) Thiourea
B) Diphenyl sulphide
C) Phenyl hydrazine
D) Benzamide
Correct Answer: A
Solution :
Blood red colour of Lassaignes extract with acid and ferric chloride indicates that both N and S are present in the compound. \[\underset{\begin{smallmatrix} sodium \\ sulphocyanide \end{smallmatrix}}{\mathop{3NaCNS}}\,+FeC{{l}_{3}}\xrightarrow{{}}3NaCl\]\[+\underset{\begin{smallmatrix} ferricsulphocyanide \\ \left( blood\text{ }red\text{ }colour \right) \end{smallmatrix}}{\mathop{Fe{{(CNS)}_{3}}}}\,\] The formulae of the given compounds are as follows: [a] Thiourea: \[N{{H}_{2}}-CS-N{{H}_{2}}\] [b] Diphenyl sulphide: \[{{C}_{6}}{{H}_{5}}-S-{{C}_{6}}{{H}_{5}}\] [c] Phenylhydrazine: \[{{C}_{6}}{{H}_{5}}-NHN{{H}_{2}}\] [d] Benzamide: \[{{C}_{6}}{{H}_{5}}-CON{{H}_{2}}\] Therefore, thiourea will show mentioned test.
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