Sodium ethoxide is obtained by the reaction of ethyl alcohol with ____.

For the reaction

${\mathrm{C}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{5}}\mathrm{OH} + \mathrm{HX} \stackrel{}{\to }{\mathrm{C}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{5}}\mathrm{X}+{\mathrm{H}}_{\mathrm{2}}\mathrm{O}$

The order of reactivity of halogen acids is ______.