Thermodynamics of Equilibrium

Which of the following fluoro-compounds is most likely to behave as a Lewis base?   

The following equilibrium are given ${\mathrm{N}}_2+3{\mathrm{H}}_2\rightleftharpoons 2{\mathrm{NH}}_3 -\dots \dots ...{\mathrm{K}}_1$
${\mathrm{N}}_2+{\mathrm{O}}_2\rightleftharpoons 2\mathrm{NO} ----{\mathrm{K}}_2$
${\mathrm{H}}_2+\frac{1}{2}{\mathrm{O}}_2\rightleftharpoons {\mathrm{H}}_2\mathrm{O}$ $-----{\mathrm{K}}_3$
The equilibrium constant of the reaction $2{\mathrm{NH}}_3+\frac{5}{2}{\mathrm{O}}_2\rightleftharpoons 2\mathrm{NO}+3{\mathrm{H}}_2\mathrm{O},$ in terms of ${\mathrm{K}}_1,{\mathrm{K}}_2$ and ${\mathrm{K}}_3$ is: