Question

How will you distinguish between (c2h5)2nh and c2h5nh2 ?

Answer 1

This class of the compounds given are amines and all that you need to know is how different classes of amines are distinguished.

That is to say that primary amines, secondary amines and tertiary amines do give a characteristic observation when tested with nitrous acid.

(C₂H₅)₂NH is a secondary amine. When it is reacted with nitrous acid, there is a formation of a yellow oily  precipitate known as nitrosamine.

C₂H₅NH₂ is a primary amine and when it is reacted with nitrous acid there is a vigorous reaction with evolution of a gas. This gas is nitrogen.