What is the primary cause of diffusion? some substances can dissolve in solvents heat added to a substance random internal motion of atoms and molecules attraction of opposite atomic charges

random internal motion of atoms and molecule

Explanation:

The primary cause of diffusion is the random internal motion of atoms and molecules.

Randomness of atoms and molecules results in diffusion.

Diffusion is the movement of particles from a region of high concentration to that of lower concentration. Substances often tend to spread out over the concentration gradient. Therefore, they have this propensity to be randomized.

C) the increase in atmospheric pressure pushes the walls of the balloon outward thus making it  is the answer.hope i you.