The way you would solve this problem is to look at the polarity of the molecules-- which has to deal with the electronegativity of the atoms themselves, and the atomic size and mass. Polarity affects intermolecular forces and causes molecules and atoms to deviate from the ideal behavior. H2 would be expected to behave most ideally because it has a dipole moment of 0 (non-polar). Also, it has smaller mass, it is not as easily polarizable. F2 may behave ideally, because it has a dipole moment of 0 also. But, it\'s mass is bigger and it is highly electronegative HF would be expected to deviate because it has a higher dipole moment, and it\'s polar. That dipole moment creates an intermolecular force that influecnes other polar molecules. Source(s): General Chemistry 4th edition (Hill, Petrucci, McCreary, Perry) Solution The way you would solve this problem is to look at the polarity of the molecules-- which has to deal with the electronegativity of the atoms themselves, and the atomic size and mass. Polarity affects intermolecular forces and causes molecules and atoms to deviate from the ideal behavior. H2 would be expected to behave most ideally because it has a dipole moment of 0 (non-polar). Also, it has smaller mass, it is not as easily polarizable. F2 may behave ideally, because it has a dipole moment of 0 also. But, it\'s mass is bigger and it is highly electronegative HF would be expected to deviate because it has a higher dipole moment, and it\'s polar. That dipole moment creates an intermolecular force that influecnes other polar molecules. Source(s): General Chemistry 4th edition (Hill, Petrucci, McCreary, Perry).