Which one has higher melting or boiling point and why?SiH4 or CH4?

As mentioned above the mp/bp of SiH4 (silane) is greater than CH4. The only attractive forces between these nonpolar molecules are induced-dipole induced-dipole forces, otherwise known as London dispersion forces. The strength of these forces increases with the number of polarizable electrons and therefore usually increase with molecular weight of the molecule hence bpSiH4 > bpCH4. The electrons on Si are more easily distorted a requirement for these weak forces.