How do you do these Redox Chem questions?

Question

Assign oxidation numbers to each atom in the following ions and molecules:

a. HPO4^2-

b. K2Cr2O7

c. BaH2

d. K2O2

Balance the following equation using the oxidation states method:

Cu + HNO3 --> Cu(NO3)2 + H2O + NO

Answer 1

H = +1 ; P = +5 ; O = -2

K = +1 ; Cr = +6 ; O = -2

Ba = +2 ; H * -1

K = +1 ; O = -1

3 Cu + 8 HNO3 >> 3 Cu(NO3)2 + 2 NO + 4 H2O