A spherical gel capsule of 0.50 cm diameter is used a drug delivery device. Initially, there is a total drug amount 0.005 mmole uniformly loaded into the gel material. The capsule is ingested, and within the gastrointestinal tract, the bulk con cent-ration of the drug A within the gastrointestinal fluid is equal to zero. However, there is a finite convective film mass transfer resistance in the mass-transfer process, and the convective mass- transfer coefficient for drug A around the surface of the sphere is equal to 5.0 × 10^-5 cm/s. At 37°C, the effective diffusion coefficient of drug within the gel is 3.0 × 10^-6 cm²/s, whereas the molecular diffusion coefficient of the drug in the gastro intestinal fluid is 1.5 × 10^-5 cm²/s.

a. What is the mass-transfer Biot number for the process? The Biot number (Bi) is the inverse of m in the concentration time charts. 

b. What is the molar concentration of drug A in the center of the capsule after 2.3 hours?