If density and diffusion coefficient are assumed constant, then governing equation for mass transfer of A dissolved in solid B is

A. $$\frac{{\partial {C_A}}}{{\partial t}} = {D_{AB}}.\Delta {C_A}$$

B. $$\frac{{\partial {C_A}}}{{\partial t}} = {D_{AB}}.{\Delta _2}{C_A}$$

C. $$\frac{{\partial {C_A}}}{{\partial x}} = {D_{AB}}.{\Delta _2}{C_A}$$

D. $$\frac{{\partial {C_A}}}{{\partial x}} = {D_{AB}}.{\Delta }{C_A}$$

Answer: Option B