Explanation

(a)
(i) The electrode with higher oxidation potential acts as anode and electrode with lower oxidation potential acts as cathode.
(ii) Cell reaction is spontaneous when $E_{cell}$ is positive. In case of Aand B ; oxidation potential of $A\ = - 0.03$ oxidation potential of $B\ = \ + 0.108$
Because oxidation potential of $B$ is more than $A$ so oxidation of $A$ is not possible. The cell having $A$ as anode and $B$ as cathode is not possible.
Therefore, non-spontaneous cell reaction takes place between $A$ and $B$.