On the basis of the standard reduction potential values, the strongest oxidizing agent is (assuming common values for Iron complexes):

1. A
   $[{\text{Fe(CN)}}_6{]}^{3-}$
2. B
   $[{\text{Fe(CN)}}_6{]}^{4-}$
3. C
   ${\text{Fe}}^{2+}$
4. D
   ${\text{Fe}}^{3+}$