The compound that does not give a positive test for nitrogen in Lassaigne's test is

What happens to the halogen when $AgNO_3$ is added to the Lassaigne solution acidified with $HNO_3$?

Match List-$I$ with List-$II$.

List-$I$ (Functional group detection)	List-$II$ (Change observed during detection)
$A$. Unsaturation (Baeyer's test)	$I$. Red colour appears
$B$. Alcoholic group (Ceric ammonium nitrate test)	$II$. Silver mirror appears
$C$. Aldehyde group (Tollen's reagent)	$III$. Violet colour appears
$D$. Phenolic group ($FeCl_3$ test)	$IV$. Discharge of pink colour

Choose the correct answer from the options given below:

During Lassaigne's test,if $N$ and $S$ are present individually in an organic compound,they are converted into:

When sodium fusion extract of an organic compound is boiled with iron$(II)$ sulphate solution followed by addition of concentrated $H_2SO_4$,it gives a Prussian blue colour. This confirms the presence of which element?

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.