${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{SOCl}}_2\to \mathrm{A}$

$\mathrm{A}+{\mathrm{Hg}}_2{\mathrm{F}}_2\to \mathrm{B}$

Both "A" and "B" are organic compounds then difference between molecular weights of "A" and "B" is