Arrange NF₃ ,PF₃ ,AsF₃and BiF₃ in increasing order of ionic character .Give reasons .

The ionic character of flourides of group 15 increases down the group. Ionic character depends on metallic behaviour. The metallic character increases down the group. Bismuth is a strong metal because of its small size and which leads to increase in ionisation energy. The increasing order of ionic character of trihlaides of group 15 is :
NF₃ < PF₃ < AsF₃ < BiF₃