A mixture of ${\mathrm{SO}}_3,{\mathrm{SO}}_2 \&{\mathrm{O}}_2$ gases is maintained at equilibrium in 10 liter flask at a temperature at which Kc for the reaction, $2{\mathrm{SO}}_{2\left(\mathrm{g}\right)}+{\mathrm{O}}_{2\left(\mathrm{g}\right)}\iff 2{\mathrm{SO}}_{3\left(\mathrm{g}\right)}$  is 100 ${\mathrm{mol}}^{-1} \mathrm{litre}$  At equilibrium.

a) If number of mole of ${\mathrm{SO}}_3 \& {\mathrm{SO}}_2$ in flask are same, how many moles of ${\mathrm{O}}_2$are present

b) If number of mole of ${\mathrm{SO}}_3$in flask are twice the number of mole of ${\mathrm{SO}}_2,$how many mole of ${\mathrm{O}}_2$ are present