Oxidation and reduction half- . a) 2h2 + o2 => 2h2o. oxidation half-reaction: . reduction half-reaction: . b) mno2(s) + 4hcl(aq) => mncl2(aq) + cl2(g) + 2h2o(l). oxidation half-reaction: . reduction half-reaction. 3) s(s)+ 6hno3(aq) => so3(g)+ 3h2o(l) + 6no2(g). oxidation half-reaction: . reduction half reaction: . *best response and i will become a fan to whoever me with this.*. : )

In a redox reaction, the half reduction which reduction occurs involves the element which has a charge that decreases after the reaction. The oxidation reaction involves an element with an increased charge after the reaction. We use H+ to balance H and H2O to balance O. 
1) oxidation: 2H2 + 2H2O -> 2H2O + 4H+ + 4e-   reduction: O2 + 4H+ + 4e- -> 2H2O
2) oxidation: 2Cl- --> Cl2 + 2e-   reduction: MnO2 + 4H+ + 2e- --> Mn2+ + 2H2O 
3) oxidation: S(s) + 3H2O --> SO3(g) + 6H+ + 6e-    reduction: 6NO3^- + 6H+ + 6e- --> 6NO2 + 6H2O

Which metal is less dense