The correct option is A C2H5NH2
The compound A is ethyl amine. It reacts with carbon disulphide in
presence of mercury (II) chloride to form ethyl isothiocyanate.
This
reaction is Hofmann mustard oil reaction and is given by primary amines
only. Thus it is test for primary amines. Isothiocyanates have pungent
smell similar to mustard oil.