Solute A is diffusing at unsteady state into a semi-infinite medium of pure B and undergoes a first-order reaction with B. Solute A is dilute. Calculate the concentration cA at points z = 0, 4, and 10.
a) cA(0) = cA0
b) cA(0) = cA0/2
c) cA(0) = cA0 * e(-kz/D)
d) cA(0) = cA0 * e(kz/D)