Answers

2015-03-23T09:45:31+05:30
In H2O2 is -1 because the sum of the oxidation states of the hydrogen and oxygen must be zero. 
calculation taking oxidation nu of oxygen is x
2(1) + 2x =0
2x = -2
x =-1
and in O2F2 is +1 because of more electronagetive atom F have -1 
calculation taking oxidation nu of oxygen is x
2x + 2(-1) = 0
2x = 2
x = 1
0