Using the definitions for 'oxidation' and for 'reduction', identify the exact species that is getting oxidized and species that is getting reduced in each of the following redox reactions:
a. 2 K (s) + F2 (l) --> 2 KF (s)
b. 6H+(aq) + 2Cr (s) ---> 2Cr3+ (aq) + 3H2(g)