The correct option for a redox couple is :

Redox couple:
Electrolysis is which both the oxidised and reduced species are present in solution and an inert metal dipped in the solution is required for electrical contact.
eg., Pt/Fe+3, Fe+2
(1) Redox couple does not exist when both oxidised forms involve the same element, because potential difference does not exist across the boundary.
(2) Redox couple does not exist when both reduced forms involve the same element because potential difference does not exist across the boundary
(4) Cathode is a redox couple, and anode is  redox couple, separately; but together they represent a net redox reaction.