Boiling point of phosphine (PH3) is -87.8 oC while that of silane (SiH4) is -111 oC. Phosphine has greater boiling point because

Explanation

The boiling point of a substance is influenced by its intermolecular forces. In the case of phosphine (PH3) and silane (SiH4), both are molecular compounds with covalent bonds.The primary intermolecular force in PH3 is dipole-dipole interaction due to the presence of a polar covalent bond between phosphorus and hydrogen. Phosphine molecules have a higher dipole moment compared to silane molecules.Silane, on the other hand, has weaker van der Waals forces (dispersion forces) since it is nonpolar, and there is no significant dipole moment.Therefore, option a is correct: the greater dipole moment in PH3 results in stronger intermolecular forces, contributing to a higher boiling point compared to SiH4.