See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Basicity of Amines **Key Principle:** Basicity of amines depends on the availability of lone pair electrons on nitrogen. Electron-donating alkyl groups increase electron density on $N$, enhancing basicity. **Analysis:** 1. **$CH_3NH_2$ (methylamine):** One alkyl group donates electron density to nitrogen. 2. **$CH_3CH_2NH_2$ (ethylamine):** One alkyl group, similar basicity to methylamine. 3. **$NH_3$ (ammonia):** No alkyl groups; lowest basicity among amines due to lack of electron-donating substituents. 4. **$CH_3CH_2CH_2NH_2$ (n-propylamine):** **Three carbons** in the alkyl chain provide maximum cumulative electron-donating effect through the inductive effect. **Trend:** As the alkyl chain length increases, the electron-donating inductive effect increases, making the lone pair on $N$ more available for accepting protons. $$\text{Basicity: } NH_3 < CH_3NH_2 < CH_3CH_2NH_2 < CH_3CH_2CH_2NH_2$$ **Answer:** Option (4) $CH_3CH_2CH_2NH_2$ is most basic because the longest alkyl chain provides the strongest electron-donating inductive effect, maximizing electron density on nitrogen's lone pair.