The correct order of decreasing basic strength of the given amines is:

The basic strength of amines depends on the availability of the lone pair of electrons on the nitrogen atom.Aliphatic vs. Aromatic: Aliphatic amines are stronger bases than aromatic amines because in aromatic amines like benzenamine, the lone pair on nitrogen is delocalized into the benzene ring through resonance.Aliphatic Amines: In aqueous solution, the basicity of ethyl-substituted amines follows the order: secondary ($2^{\circ }$) > primary ($1^{\circ }$). Therefore, N-ethylethanamine is stronger than ethanamine.Aromatic Amines: N-methylaniline is more basic than benzenamine because the methyl group is an electron-releasing group (+I effect), which increases the electron density on the nitrogen atom.Final order: N-ethylethanamine > ethanamine > N-methylaniline > benzenamine.