which of the following represent redox reactions?
I. `Cr_(2)O_(7)^(2-)+2overset(ө)OHrarr2CrO_(4)^(2-)+H_(2)O`
II. `Zn+CuSO_(4)rarrZnSO_(4)+Cu`
iii.`MnO_(4)^(ө)+3Mn^(2+)+4overset(ө)OHrarr5MnO_(2)+2H_(2)O`
IV. `2Cu^(o+)rarrCu+Cu^(2+)`
A. `Cr_(2)O_(7)^(2-)+2OH^(-) rarr 2 CrO_(4)^(2-)+H_(2)O`
B. `2 CrO_(4)^(2-) +2H^(+) rarr Cr_(2)O_(7)^(2-)+H_(2)O`
C. `2 MnO_(4)^(-)+3 Mn^(2+)+4 OH^(-) + 4OH^(-) rarr 5 MnO_(2)+2 H_(2)O`
D. `2 Cu^(+) rarr Cu+Cu^(2+)`
