A hypothetical electrochemical cell is shown below $\text{A}|{\text{A}}^{+}(x\text{M})||{\text{B}}^{+}(y\text{M})|\text{B}$.The emf measured is $+0.20\text{V}$. The cell reaction is :

In standard cell notation, the anode (site of oxidation) is written on the left, and the cathode (site of reduction) is written on the right.Anode reaction: $\text{A}\to {\text{A}}^{+}+e^{-}$ Cathode reaction: ${\text{B}}^{+}+e^{-}\to \text{B}$ Net cell reaction: $\text{A}+{\text{B}}^{+}\to {\text{A}}^{+}+\text{B}$. Since the emf is positive, the reaction is spontaneous as written.