Which of the following reactions are redox reactions? 4Li(s)+O2(g)→2Li2O(s) Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s) Sr(NO3)2(aq)+Na2SO4(aq)→ SrSO4(s)+2NaNO3(aq) HBr(aq)+KOH(aq)→H2O(l)+KBr(aq)

As2O3 → H3AsO4

As2O3 → 2H3AsO4             balance As

5H2O + As2O3 → 2H3AsO4       balance O by adding H2O to one side

5H2O + As2O3 → 2H3AsO4 + 4H+    balance H by adding H+ to one side

5H2O + As2O3 → 2H3AsO4 + 4 H+ + 4e-     balance charge by adding electrons to one side

Now do the same for the other part of the reaction

NO3- → NO

NO3- → NO + 2H2O

4H+ + NO3- → NO + 2H2O

3e- + 4H+ + NO3- → NO + 2H2O

Now cancel the electrons by multiplying the first equation by 3 and the second equation by 4, then add them together .

3As2O3 + 4NO3- + 7H2O + 4H+ → 6H3AsO4 + 4NO

1.solid

2.carbon dioxide

3.helium