A 20 L vessel contains 0.1 mole of $O_2$ at 300 K. $O_3$ is prepared in the vessel by subjecting $O_2$ to silent electric discharge till the volume is reduced to 15 L at 300K. What is the number of moles of $O_3$ formed?

$S{O_2}\,\, + \,\,2\,\,{H_2}S\,\, o \,\,3S\,\, + 2\,\,{H_2}O$ 2 mol of ${H_2}S$ and 11.2 L $S{O_2}$ at NTP react to form $imes$ mol at sulphur, then $imes$ is