For the following cell with hydrogen electrodes at two different pressure p₁ and p₂. What will be the emf for the given cell :

$$\eqalign{ & Pt({H_2})|{H^ + }(aq)|Pt({H_2}) \cr & \,\,\,\,\,{p_1}\,\,\,\,\,\,\,\,\,\,\,\,\,\,1M\,\,\,\,\,\,\,\,\,\,\,\,{p_2} \cr} $$

When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are :

EMF of a cell in terms of reduction potential of its left and right electrodes is :

Which of the following is a redox reaction ?