Question

what type of interactions hold the molecules together in a polar molecular solid

Answer 1

2 types of forces hold the molecules or atoms in a polar compound: van dear wal's force of attraction and intermolecular forces or hydrogen bonds.
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Answer 2

Interactions hold the molecules together in a polar molecular solid:

In a Molecular Solid there are two forces acting on the molecules to hold them together which are van-der-waal's force of attraction and intermolecular forces or hydrogen bonds

Van der Waals are generally defined as the intermolecular attraction forces.

Stronger forces are termed as dipole van der waal forces and the weak one are called London Forces.

A hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom develops and attraction force to another very electronegative atom.