The correct decreasing order of the basic strength of ethyl substituted amines and ammonia in aqueous solution is:

Step-by-step solution

In aqueous solution, the basic strength of amines depends on the combined effect of the inductive effect (+I), solvation (hydrogen bonding with water), and steric hindrance. For ethyl substituted amines, the larger size of the ethyl group compared to the methyl group causes steric hindrance to play a more significant role, altering the balance between solvation and the +I effect. The resulting order of basicity for ethylamines in aqueous solution is secondary > tertiary > primary > ammonia. Therefore, the correct d