Why substitutional diffusion is more strongly influenced by temperature than interstitial diffusion.

Explanation:

Substitutional diffusion is a mechanism in which diffusant substitutes for the host atoms by displacing them from their lattice sites and high activation energy process. Substitutional diffusants (e.g. all p- and n-type dopants in silicon) feature low diffusion coefficient.

Interstitial diffusion mechanism in which diffusant moves in between host atoms in the lattice and low activation energy process. Interstitial diffusants (e.g. gold in silicon) feature high diffusion coefficient.

So when temperature increase, there is a slight change in the number of molecules in the interstitial sites, but when compared to substitutional diffusion, the intermolecular distance plays an integral role which is a function of temperature. As the temperature increases, more thermal energy are available in substitutional diffusion thus, diffusion is higher at higher temperature.

the answer to your question is c