Aniline upon heating with conc. \(HNO_3\) and conc. \(H_2SO_4\) mixture gives

Black tarry mass

The correct answer is option 3. Black tarry mass.

When aniline is treated with a mixture of concentrated nitric acid (\(HNO_3\)) and concentrated sulfuric acid (\(H_2SO_4\)), it undergoes nitration. However, if the reaction conditions are harsh or not carefully controlled, several side reactions can occur.

Under severe conditions, such as high temperature or prolonged heating, aniline can undergo complex reactions, including polymerization and decomposition. The concentrated acids can also lead to dehydration and oxidation of the organic molecules present, resulting in the formation of a complex mixture of products.

The formation of a black tarry mass indicates that the reaction has resulted in the production of a highly viscous and dark-colored substance, which is likely a mixture of polymers, decomposition products, and other organic compounds formed during the reaction. This black tarry mass is often difficult to characterize and may contain a variety of compounds.

So, in this scenario, the harsh reaction conditions lead to the formation of a complex mixture of products, resulting in the observation of a black tarry mass rather than a specific organic compound.

Therefore, the correct answer is indeed 3. Black tarry mass.