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

CONCEPT:

Basic Strength of Amines

• The basic strength of amines depends on the availability of the lone pair of electrons on the nitrogen atom for protonation.
• Electron-donating groups (EDGs) increase the availability of the lone pair, thereby increasing basicity, while electron-withdrawing groups (EWGs) decrease basicity.
• For aromatic amines, resonance effects reduce the availability of the lone pair on nitrogen, making them less basic compared to aliphatic amines.
• For aliphatic amines, steric hindrance and the inductive effect of alkyl groups also affect the basic strength.

EXPLANATION:

Lower is the value of pK_b, higher is the basicity.

Also, aliphatic amines are stronger bases than aromatic amines.

pK_b : Benzenamine > N-Methylaniline > Ethanamine > N-Ethylethanamine

Basic strength : N-Ethylethanamine > Ethanamine > N-Methylaniline > Benzenamine

• N-methylaniline: The nitrogen is part of an aromatic ring, and the lone pair of electrons on nitrogen is delocalized into the ring through resonance, reducing its availability for protonation. This makes it less basic.
  
• Benzenamine: Similar to N-methylaniline, its lone pair is delocalized into the aromatic ring, making it less basic than aliphatic amines.
  
• Ethanamine: This is a simple aliphatic amine where the lone pair on nitrogen is readily available for protonation. It is more basic than aromatic amines.
• N-ethylethanamine: This is a secondary aliphatic amine, and the presence of two alkyl groups provides a stronger inductive effect, increasing the availability of the lone pair. It is the most basic among the given compounds.
  

The correct order of decreasing basic strength is N-ethylethanamine > ethanamine > N-methylaniline > benzenamine