What are the nature of amines? 

Basic 

The correct answer is option is 2. Basic.

Amines are organic compounds derived from ammonia \((NH_3)\) by replacing one or more hydrogen atoms with alkyl or aryl groups. They are characterized by the presence of a nitrogen atom bonded to one or more carbon atoms. Amines exhibit basic properties due to the presence of a lone pair of electrons on the nitrogen atom.

Basic Nature of Amines:

1. Lone Pair of Electrons: The nitrogen atom in amines has a lone pair of electrons, making it capable of accepting a proton \((H^+)\) to form a positively charged ammonium ion \((NH_4^+)\). This lone pair is available for donation to a proton, enabling the amine to act as a Lewis base.

2. Proton Acceptance: Amines can undergo protonation reactions, where they react with acids to form ammonium salts. In this reaction, the lone pair on the nitrogen atom forms a coordinate bond with a proton from the acid, resulting in the formation of an ammonium ion.

\(\text{R-NH}_2 + \text{H}^+ \rightarrow \text{R-NH}_3^+\)

3. Basicity Trends: The basicity of amines depends on factors such as the electronic effects of substituents attached to the nitrogen atom, the size of alkyl groups, and the presence of aromatic rings. Generally, primary and secondary amines are more basic than tertiary amines. In primary and secondary amines, the lone pair of electrons is more available for protonation due to less steric hindrance.

4. Amphoteric Behavior: While amines primarily act as bases, certain aromatic amines can exhibit weak acidic behavior due to the resonance stabilization of the conjugate acid. However, the acidic nature of amines is generally much weaker compared to their basic nature.

In summary, amines are known for their basic nature due to the presence of a lone pair of electrons on the nitrogen atom, which enables them to accept protons and form ammonium ions. This basicity is a fundamental property of amines and plays a crucial role in their reactivity and applications in various chemical reactions.