An acid is any substance that
a: increases a solution's ph
b: produces hydroxide ions
c: donates a proton
d: acts as a hydrogen acceptor

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

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