In the production of long 0.2 cm x 0.2 cm square polymer rods, small amounts of monomer residue are distributed throughout the rods in a concentration of 10-4 mol/cm3 . this trace residue is to be removed by extraction with a solvent in an agitated bath in which the external mass transfer coefficient is high enough that it can be considered to be effectively infinite. if the diffusion coefficient of the monomer in the rod is 10-5 cm 2 /s, evaluate the time required to reduce the concentration of the monomer along the center line of the rod to (a) 50 percent, (b) 1 percent of its initial value.