The Nernst equation is used to calculate the equilibrium constant \( K_c \) from the cell potential \( E^\circ_{\text{cell}} \):
\[
E^\circ_{\text{cell}} = \frac{0.059}{n} \log_{10} K_c
\]
Where:
- \( n \) is the number of moles of electrons transferred in the reaction (which is 2 for this reaction),
- \( E^\circ_{\text{cell}} \) is the standard cell potential,
- \( K_c \) is the equilibrium constant.
Rearranging the equation to solve for \( \log_{10} K_c \):
\[
\log_{10} K_c = \frac{E^\circ_{\text{cell}} \cdot n}{0.059}
\]
Substituting \( E^\circ_{\text{cell}} = x \) and \( n = 2 \), we get:
\[
\log_{10} K_c = \frac{2x}{0.059}
\]
Thus, the correct answer is (3) \( \frac{2x}{0.059} \).