1. An elementary reaction A  B is conducted using a spherical pellet impregnated with platinum throughout the pellet. The reactant concentration halfway to the center of the pellet is 10% of the concentration at the surface. The effective diffusivity and the surface concentration values are De: 0.1 cm2/s, [A]s: 0.001 mol/L. The radius of the pellet is 10 m. What is the reactant concentration at a depth of 2.5 m from the surface? To what diameter should the pellet be reduced if the effectiveness factor is to be 0.8?