The blue color obtained in the Lassaigne's test is due to the formation of which compound?

The fusion of sodium with an organic compound containing nitrogen gives mainly:

Three students,Manish,Ramesh,and Rajni were determining the extra elements present in an organic compound given by their teacher. They prepared the Lassaigne's extract $(L.E.)$ independently by the fusion of the compound with sodium metal. Then they added solid $FeSO_4$ and dilute sulphuric acid to a part of the Lassaigne's extract. Manish and Rajni obtained prussian blue colour,but Ramesh got red colour.
Ramesh repeated the test with the same Lassaigne's extract,but again got red colour only. They were surprised and went to their teacher and told him about their observation. Teacher asked them to think over the reason for this. Can you help them by giving the reason for this observation? Also,write the chemical equations to explain the formation of compounds of different colours.

Match Column $-I$ with Column $-II$.

Column $-I$	Column $-II$
$(A).$ Dumas method	$(3).$ Nitrogen gas
$(B).$ Kjeldahl's method	$(5).$ Ammonium sulphate
$(C).$ Carius method	$(1).$ $AgNO_3$
$(D).$ Chromatography	$(2).$ Silica gel
$(E).$ Homolytic fission	$(4).$ Free radical

Lassaigne's test for the detection of nitrogen fails in

Give the answers for the Lassaigne test:
$(i)$ If nitrogen and sulphur are both present,what observation is observed?
$(ii)$ If bromine is present,what is the observation?
$(iii)$ In the Lassaigne extract,if black precipitates are not obtained upon adding $CH_3COOH$ and lead acetate,what does this indicate?
$(iv)$ What is the reason for adding $FeSO_4$ to the Lassaigne extract?
$(v)$ Why is the Prussian blue colour observed?
$(vi)$ What does the violet colour with sodium nitroprusside in the Lassaigne extract indicate?