The Nernst equation for a galvanic cell at 25°C is:

• A. E = E°cell − (0.05916/n) log10(Q)
• B. E = E°cell + (0.05916/n) log10(Q)
• C. E = E°cell − (0.05916) log10(Q) / n
• D. E = E°cell − (0.594/n) log10(Q)

Answer: (A)

The key idea is that the Nernst equation links the actual cell potential to the standard potential and the reaction quotient, with a temperature-dependent factor that converts the natural logarithm to base-10 logarithm. At 25°C, that factor is 0.05916 V per electron transferred, and the equation carries a minus sign.

So the correct form is E = E°cell − (0.05916/n) log10(Q). The minus sign means the cell potential decreases as Q increases (more products relative to reactants). By definition, Q = activity of products over activities of reactants, with solids and pure liquids omitted. When Q = 1, E = E°cell, and as the reaction shifts toward products (Q grows), E drops accordingly.

The other options are off for these reasons: a plus sign would imply the potential increases with Q, which isn’t correct for a galvanic cell; using 0.594 instead of 0.05916 is off by a factor of 10; and a form that rearranges the same factors is generally written in the standard way above, which is the conventional presentation.