6. The Nobel Prize in chemistry 2010 was awarded to "Palladium-catalyzed cross-coupling reactions in organic synthesis". Please give the **oxidation state** of **palladium** in each of the following transition-metal catalysts. (4%)
(A)\( PdCl_2 \)
(B)\( Pd(OCOCH_3)_2 \)
(C)\( Pd(OCOCF_3)_2 \)
(D)\( Pd(PPh_3)_4 \)