Based on selective permeability, if the pores in the dialysis tubing were too small to allow iodine potassium to pass through, the liquid in the tubing would not turn black.
What is Selective permeability
Selective permeability refers to the ability of a membrane to allow some molecules to pass through it but no others.
In the dialysis tubing, selective permeability is used to remove some substances but not others.
The selective permeability of the dialysis tubing depends on the pore size.
When a dialysis tubing containing starch solution was dipped into a beaker containing iodine, the solution in the tubing turned black due to the ability of iodine molecules to pass through the membrane.
However, if the pores in the dialysis tubing were too small to allow iodine potassium to pass through, the liquid in the tubing would not turn black.
Learn more about selective permeability at: selective permeability