oxidation and reducing reactions?

Question

which element is oxidized and which element is reduced in each of the following reactions

a) K2 Cr2 O7 + 14HI -->> 2KI + 2CrI3 + 3I2 + 7H20


b) Cu + 2AgNo3 ---> Cu(NO3)2 + 2Ag

C) Na2SO4 + 4C -> Na2S + 4CO

Answer 1

a) Cr(VI) is reduced and I- is oxidized.

b) Cu is oxidized and Ag(I) is reduced

c) S(VI) is reduced and C is oxidized.