In the Lassaigne sodium fusion test,$N$ and $S$ of an organic compound are converted into:

Why is nitric acid $(HNO_3)$ added to sodium extract before adding silver nitrate $(AgNO_3)$ for testing halogens?

Lassaigne's test for nitrogen is negative for which compound?

Appearance of blood red colour,on treatment of the sodium fusion extract of an organic compound with $FeSO_4$ in presence of concentrated $H_2SO_4$ indicates the presence of element/s

Assertion : During the test for nitrogen with Lassaigne's extract,on adding $FeCl_3$ solution,sometimes a blood-red coloration is obtained.
Reason : Sulphur is also present along with nitrogen in the organic compound.

In Lassaigne's extract of an organic compound,both nitrogen and sulphur are present,which gives blood red colour with $Fe^{3+}$ due to the formation of-