Which of the following bases is the strongest in an aqueous medium?

1. CH3NH2
3. (CH3)2NH
4. C6H5NHCH3

Hint: Inductive effect and solvation effect .
Compounds Factors responsible for
basic character are
CH3-NH2 Inductive effect (+ I)
NC-CH2-NH2 Inductive effect (- I)
(CH3)2NH Inductive effect (+ I) and Solvation
- I effect and resonance

Since, + I effect and solvation increases basic character while —I effect and resonance decreases basic character. Hence, the correct option is 3.