Which is expected to have the lowest vapor pressure?

Question

Which is expected to have the lowest vapor pressure?

CH4

SiH4

NH3

PH3

H2O

Answer 1

H2O

The substance with the strongest intermolecular forces would be expected to have the lowest vapor pressure.

Both NH3 and H2O exhibit hydrogen bonding whereas the others have only dispersion and/or dipole-dipole interactions. Between NH3 and H2O, H2O will have stronger intermolecular forces because the number of hydrogen bonds between molecules is greater than it is for NH3.