Of the interhalogen $A{X}_3$ compounds, ${\mathrm{ClF}}_3$ is most reactive but $Br{F}_3$ has higher
conductance in liquid state. This is because

Electrical conductance does not depend on concentration.

 ${\mathrm{BrF}}_3$ has higher molecular mass

 $Br{F}_3$ dissociates into ${\mathrm{BrF}}_2^{+}\text{and }{\mathrm{BrF}}_4^{-}$ most easily

 ${\mathrm{ClF}}_3$ is more volatile