As we know that theLassaigne’s extract is prepared to detect the presence of N, S, Halogens and P.
As when the Lassaigne’s extract is prepared, it allows all the elements present in the particular compound to come into the elemental state, so that they can easily be detected.
Now, the reaction involved is for Nitrogen estimation:
Na + C + N→ NaCN
NaCN + FeSO4 + dilute sulphuric→ Fe4[FeCN6]3 (Prussian blue colour solution)
The reaction involved is for sulphur estimation:
Na + C + N + S → NaCNS
3NaCNS + FeSO4 + dilute sulphuric→ Fe(CNS)3 (Blood red colour) + 3Na+
Hence, the Ramesh has N as well as S present in his organic compound so, he was getting the Blood red colour of Fe(CNS)3 and Manish and Rajni were having only Nitrogen in their compound, hence they got Prussian blue colour.
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