`NH_3` is more basic than `NF_3`.
In `NF_3, N` is less electronegative than `F`, hence bond pair shifts more towards `F`, thereby `delta` positive charge density on `N` increases, hence tendency to donate electron decreases. In `NH_3, N` is more electronegative than `H`, hence bond pair shifts towards `N` in `N-H`, thereby negative charge density on `N` increases, hence tendency to donate electrons increases. Hence `NH_3` is more basic as compared to `NF_3`.
