Which equation represents the emf of a cell in terms of its composition?

The equation that represents the electromotive force (emf) of a cell in terms of its composition is derived from the relationship between Gibbs free energy and cell potential. The correct option shows the relationship in the form where the standard cell potential is adjusted for the reaction quotient, Q.

In thermodynamics, the Nernst equation is commonly used to relate the cell potential (E) to the concentrations (or partial pressures) of the reactants and products involved in an electrochemical reaction. Here, E represents the actual cell potential, (E^\circ) is the standard cell potential at standard conditions, R is the universal gas constant, T is the temperature in Kelvin, ν is the number of moles of electrons transferred in the electrochemical reaction, and F is Faraday's constant. The reaction quotient Q expresses the ratio of the concentrations (or activities) of the products to the reactants at any given moment.

The equation shows that the cell potential decreases logarithmically from its standard state as the reaction shifts towards equilibrium. The subtraction of the term ((RT/νF) \ln Q) indicates that as the concentration of products increases (and thus Q increases), the cell potential decreases, reflecting Le Chatelier's principle where