Thermal diffusivity is defined as the ratio of heat conducted to the heat energy stored per unit volume of a material.It describes how fast heat can be transferred across themedium.

ŸGreater the value of thermal diffusivity,faster is the propagation of heat through the medium

ŸWhen thermal conductivity (k) increases then thermal diffusivity (a) increases. In case of super conductor,  

Hence, the correct option is (D).