Question

Use the changes in oxidation numbers to identify which atoms are oxidized and which are reduced in each reaction.

Answer 1

You didn't include much information as to what you were referring too, however I answered a similar question recently to a friend so I'm hoping this is the same question in complete as to yours, if not I apologize.

a.) 2Na(s) + Cl2(g) -----> 2NaCl(s) 
Na --> Na+1 is oxidized 
Cl2 --> Cl- is reduced 

b.) 2HNO3(aq) + 6HI(aq) ----> 2NO(g) + 3I2(s) + 4H2O(l) 
N+5 --> N+2 is reduced 
I-1 --> I2 is oxidized