Fick's second law of diffusion is stated as:

A. $$\frac{{\partial C}}{{\partial T}} = D.\frac{{{\partial ^2}C}}{{\partial {x^2}}}$$

B. $$\frac{{\partial C}}{{\partial x}} = D.\frac{{{\partial ^2}C}}{{\partial {t^2}}}$$

C. $$\frac{{\partial C}}{{\partial t}} = \frac{\partial }{{\partial x}}\left( {D.\frac{{\partial C}}{{\partial t}}} \right)$$

D. $$\frac{{\partial C}}{{\partial t}} = \frac{\partial }{{\partial t}}\left( {D.\frac{{\partial C}}{{\partial x}}} \right)$$

Answer: Option A