The size of N atom is less than the size of the P atom. So the electron density on the N atom is more than that on the P atom. Hence it becomes a stronger base i.e. it extracts H+ easily which makes it have a higher proton affinity than PH3. Hope it helps. 1.6k Views ยท View Upvoters · Aniruddh Ramanujam, studied at Smt. read more