A. RNH2 > R2NH > R3N
B. R2NH > R3N > RNH2
C. R3N > R2NH > RNH2
D. R2NH > RNH2 > R3N
I had been asked this question in an international level competition.
This interesting question is from Amines Chemical Reactions topic in division Amines of Chemistry – Class 12
The explanation is: There is a subtle interplay of inductive effect, solvation effect and stearic hinderance of alkyl groups to determine the order of basicity of alkylamines in aqueous solutions. For ethyl substituted amines, it is 2°>3°>1°