# Arrange $Cl, F,F^{-},Cl^{-}$ in the increasing order of ionisation potential ?
$\begin{array}{1 1} F^{-} < CL^{-} < CL < F \\ CL^{-} < F^{-} < CL < F \\ CL^{-} < F^{-} < F < CL \\ F^{-} < CL^{-} < F < CL \end{array}$