The reason salt crystals, such as kcl, hold together so well is because the cations are strongly attracted to

The answer is anions. Cations are positively-charged ions (in this case K+) while anions are negatively-charged ions (in this case Cl-). The ions attract each other  through electrostatic charges and arrange themselves in an ordered fashion to form a lattice

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