Assign reasons for the following:
Ammonia (NH₃) has greater affinity for protons than phosphine (PH₃).

In PH₃ the size of nitrogen is smaller than the size of phosphorus in PH₃, hence in NH₃ the lone pair of electrons is concentrated on a small region, so its density per atom is more.  On other hand phosphours is larger n size and also have vaccant d- orbital it shift electron to d thus lesser avaliable to donation of electron. Due to this reason NH₃ has greater affinity towards a proton, i.e. it would be more basic than PH₃.