During Lassaigne's Test for Nitrogen a Blood?

The formation of blood red colouration during Lassaigne's test indicates the presence of both N and During fusion, sodium thiocyanate is formed which gives blood red colouration with FeCl3.

How is nitrogen detected by Lassaigne'S test?

The extract is boiled with FeSO4 and acidified with concentrated H2SO4. The appearance on Prussian blue colour indicates the presence of nitrogen.

Which gives blood red colour while doing Lassaigne'S test for nitrogen?

Hint : The presence of Nitrogen and Sulphur in the organic compound will result in reaction to form thiocyanate in the Lassaigne test. This product formed on heating with $FeS{O_4}$ or $FeC{l_3}$ gives out a complex which has red colour.