we are going to use this formula:
E° = 0.0592/ n * ㏒K
when E° is the standard state cell potential
and n is number of moles of electrons transferred in the balanced equation
for the reaction of the cell.
Sr(s) + Mg2+ (aq) ↔ Sr2+(aq) + Mg(s)
we can get it by using the given balanced equation, we here have 2 electrons
transferred so, n = 2
and K the equilibrium constant = 3.69 x 10^17
so, by substitution:
∴ E° = 0.0592 / 2 * ㏒ (3.69 x 10^17)
= 0.52 V