Match List - I with List – II 

List-I (Element detected)	List-II (Product formed)
A)  $N$	I.  $AgX$
B)  $S$	II. ${\left(N{H}_4\right)}_{3}P{O}_4.12Mo{O}_3$
C)  $P$	III. $N{a}_4\left[Fe{\left(CN\right)}_{5}NOS\right]$
D)  $X_{(x=Cl,Br.I)}$	IV. $F{e}_4{\left[Fe{\left(CN\right)}_6\right]}_3$

The Correct Match is

The final product formed is ferri-ferro cyanide$F{e}_4{\left[Fe{\left(CN\right)}_6\right]}_3$ in nitrogen detection.

During the preparation of Lassaigne's extract, sulphur from the organic compound reacts with sodium to form sodium sulphide. It gives a purple colour with sodium nitroprusside due to the formation of sodium thionitroprusside$N{a}_4\left[Fe{\left(CN\right)}_{5}NOS\right]$.

A yellow precipitate or colour indicates the presence of phosphorus (due to the production of ammonium phosphomolybdate-${\left(N{H}_4\right)}_{3}P{O}_4.12Mo{O}_3$) during phosphorous detection.

Halogen in organic compounds is detected by the Carius method. Masses of organic compounds are heated with fuming nitric acid in the presence of silver nitrate in the Carius tube. Carbon and hydrogen are oxidized to carbon dioxide and water. The halogens present form silver halides ($AgX$) and are finally weighed.