Consider potassium ions crossing a biological membrane 10 nm thick. The diffusion coefficient for potassium in the membrane is 1.0 1016 m2/s. (a) What is the net number of potassium ions per second that will move across an area 100 nm x 100 nm if the concentration difference across the membrane is maintained at 0.50 mol/liter? Give your answer as a positive number in units of numbers of ions