If the pK_b value of N,N-diethylethanamine is 3.25. What will be the pK_b value of ethanamine.

3.29

The correct answer is option 4. 3.29.

In ethyl substituted amines (aqueous), the inductive effect has a bigger role than the solvation effect (because the size of ethyl is larger than methyl group), and as a result the basic strength of N,N-diethylethanamine will be higher than that of ethanamine. Thus, the pK_b value of the latter will be very slightly higher than the former.