Consider the reaction$($T $=900$C$,$ P $=1$atm$)$ Fe$3$O$4($s$)+4$H$2($g$)-3$Fe$($s$)+4$H$2$O$($g$),$ neglecting the ash layer diffusion resistance, calculate the time for the Fe$3$O$4$ particle size to decrease from $5$mm to $1\mathrm{.}25$mm$?$ concentration of H$2=4\%($v$/$v$).$ bulk density of Fe$3$O$4=5000$kg$/$m$3,$ M$($Fe$3$O$4)=230.$