Final answer:
The boiling points of the molecules can be arranged in increasing order based on the strength of their intermolecular forces.
Step-by-step explanation:
The intermolecular forces in these molecules can be determined to identify their boiling points. PH3 (phosphine) has dipole-dipole forces, Cl2 (chlorine) has London dispersion forces, H2O (water) has hydrogen bonds, and CH4 (methane) has only London dispersion forces. Hydrogen bonds are stronger than dipole-dipole forces, which are stronger than London dispersion forces. So, the molecules can be arranged in increasing boiling point as follows: CH4 < Cl2 < PH3 < H2O.