The correct option is C diethyl amine
Secondary amines(−NH group containing amines), when reacts with nitrous acid (HNO2), a yellow oily nitroso compound is formed.
Hence, only diethyl amine forms a yellow oily liquid with HNO2.
(C2H5)2NHdiethylamine+HNO2→(C2H5)2N−N=ON−nitrosodiethylamine(yellowoilyliquid)