Which of the following is strong base?

Explanation

The correct answer is R₂NH because secondary amines (R₂NH) are generally stronger bases than primary amines (RNH₂) and ammonia (NH₃). This is due to the presence of additional alkyl groups that donate electron density to the nitrogen atom, enhancing its ability to donate a lone pair of electrons. In contrast, NH₃ is a weak base as it does not completely ionize in solution. PH₃ is even weaker than NH₃ because phosphorus is less electronegative than nitrogen and forms weaker hydrogen bonds. Primary amines, RNH₂, are intermediate in strength, as they have only one alkyl group to donate electron density.