The pronounced change from non-metallic behaviour and also increase in the basicity of oxides from nitrogen to bismuth in group `15` is principally due to incresing size of the atoms. The ionisation potential of nitrogen is very high on account of its small size. However, ionisation potential decreases regularly on descending the group.
Which trihalide is most ionic among the following ?
A. `NCl_3`
B. `PCl_3`
C. `BiF_3`
D. `SbF_3`
