In the following reaction,2H2S(g)  +SO2(g) →  3S(s) + 2H2O(l)One equivalent of H2S(g) will reduce

Chang in oxidation number of S of H2S = 2 unitsChange in oxidation number of S of SO2=4unitsThen one mole H2S = 2 equivalents H2SOne mole SO2 = 4 equivalent SO2One equivalent H2S =one  equivalent SO2=0.25  mole  SO2