Question

why down the group basicity decreases but nucleophilicity increases​

Answer 1

Answer:

In group 15, the hydrides of the formula XH3 have a lone pair on the central atom. As we go down the group, size of the atom increases. And hence, ELECTRON DENSITY OVER THE GROUP 15 ELEMENT DECREASES. That's why the tendency to donate electrons decreases, hence basicity decreases down the group.

Answer 2

Answer:

In group 15, the hydrides of the formula XH3 have a lone pair on the central atom. As we go down the group, size of the atom increases. And hence, ELECTRON DENSITY OVER THE GROUP 15 ELEMENT DECREASES. That's why the tendency to donate electrons decreases, hence basicity decreases down the group.