75.0 g of PCl 5(g) is introduced into an evacuated 3.00 L vessel and allowed to reach equilibrium at 250ºC. PCl 5(g) PCl 3(g) + Cl 2(g) If K p = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium?

Yes you are correct use the scientific method

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   

Can i get a picture of the passage