Nitrogen can be estimated by Kjeldahl's method for which of the following compounds?

Which of the following compounds is not expected to show Lassaigne's test for nitrogen?

In the Lassaigne's test for nitrogen in an organic compound,the Prussian blue colour is obtained due to the formation of:

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.

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

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-