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

For testing halogens in an organic compound with $AgNO_{3}$ solution,sodium extract (Lassaigne's test) is acidified with dilute $HNO_{3}$. What will happen if a student acidifies the extract with dilute $H_{2}SO_{4}$ in place of dilute $HNO_{3}$?

Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

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

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

The gases respectively absorbed by alkaline pyrogallol and oil of cinnamon are: