Chemical driving force

Which of the following concentration gradients has the greatest chemical driving force?

a. A concentration of 10 mM in the ICF and 5 mM in the ECF

b. A concentration of 70 mM in the ICF and 260 mM in the ECF

c. A concentration of 50 mM in the ICF and 250 mM in the ECF

d. A concentration of 100 mM in the ICF and 20 mM in the ECF