Electrode potential for Mg electrode varies according to the equation

. The graph of vs log [Mg²⁺] is

The given equation is the Nernst equation. Here is the cell potential at a given concentration and log [Mg²⁺] is the log of the concentration of Mg²⁺. They are directly proportional to each other as increase in concentration leads to an increase in cell potential.

The given equation is equivalent to equation of straight line y = mx + c. Hence, the graph will be a straight line with as the y-intercept and a positive slope 0.059/2.

The equation is arranged in the y = mx+c form as = . The correct option is (ii).