Final answer:
The equilibrium potential for K at 20°C cannot be calculated without specific concentration values for potassium ions inside and outside the cell, though it is known to depend on the concentration. The correct answer is option (a).
Step-by-step explanation:
To calculate the equilibrium potential for K (potassium) at 20°C, we can use the Nernst equation. However, the question does not provide specific concentrations of potassium ions inside and outside the cell to use in the calculation.
Generally, the Nernst equation at 25°C (298 K) for a monovalent ion like K+ is E = E0 - (0.0591 V / n) * log([K+]out/[K+]in), where E0 is the standard reduction potential, n is the number of electrons transferred in the half-reaction (in this case 1 for K+), and [K+]out/[K+]in are the concentrations of potassium ions outside and inside the cell respectively.
Without the specific concentration values, we cannot provide a numerical answer. Therefore, the correct answer is that the equilibrium potential for K depends on concentration.