2012 Unit 4 Chem Exam Q7c

[stevos2151]

The solutions say the answer should be 

O2 + 4H+ + 4e --> 2H20

But I don’t see why the answer couldn’t be

O2 + 2H+ +2e --> H2O2

or

O2 + 2H2O + 4e --> 4OH-

Any help would be appreciated