The tendency of molecules to move toward areas of lower concentration is called
a. suffusion
b. diffusion
c. suspension
d. effusion

The correct answer is B. The tendency of molecules to move toward areas of lower concentration is called diffusion. This happens when there is a concentration gradient. This is described by the Fick's laws of diffusion. Diffusion is the net movement of molecules from a higher concentration to lower concentration to achieve equilibrium.

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf