Final answer:
The boiling point of CH₄ is lower than that of SiH₄ because of the difference in molar mass.
Step-by-step explanation:
Applying the skills acquired in the chapter on chemical bonding and molecular geometry, all of these compounds are predicted to be nonpolar, so they may experience only dispersion forces: the smaller the molecule, the less polarizable and the weaker the dispersion forces; the larger the molecule, the larger the dispersion forces. The molar masses of CH4, SiH4, GeH4, and SnH4 are approximately 16 g/mol, 32 g/mol 77 g/mol and 123 g/mol respectively. Therefore, CH4 is expected to have the lowest boiling point and SnH4 the highest boiling point.