Balancing equation in chemistry

Question

how could i balance this equation by oxidation no. method. Indicating oxidizing agent, reducing agent, the atom oxidized and the atom reduced.

a. NH3 O2 ---> NO H2O

b. P 02 -----> P4O10

c. Cr2O-7 Cl- H -----> Cl2 H2O Cr 3

Answer 1

a O2 oxidizes NH3 / is reduced by it. N -oxidized, O-reduced

4NH3 + 5 O2 = 4NO + 6H2O

b O2 oxidizes P. O - reduced, P- oxidized

4P + 5O2 = P4O10

c Cr2O7-- oxidizes Cl- Cr+6 becomes Cr+3 and Cl- becomes Cl0

Cr2O7-- + 6Cl- + 14H+ = 2Cr3+ + 3Cl2 + 7H2O