0.5 mole each of ${\mathrm{H}}_2\mathrm{S}$and ${\mathrm{SO}}_2$ are mixed together in a reaction flask,react according to equation:$2{\mathrm{H}}_2\mathrm{S}+{\mathrm{SO}}_2\to 2{\mathrm{H}}_2\mathrm{O}+3\mathrm{S}.$Number of moles of Sulphur formed is 

From the equation 2 moles of ${\mathrm{H}}_2\mathrm{S}$reacts with 1 mole of ${\mathrm{SO}}_{2 }$to give 3 mole of $\mathrm{S}.$

0.5 mole ${\mathrm{H}}_2\mathrm{S}$combines with 0.25 mole of ${\mathrm{SO}}_{2 }$to form  0.75 mole of $\mathrm{S}.$