What type of interactions hold together the molecules in a polar crystalline solid ?

Explanation

### Step-by-Step Solution

1. **Understanding Polar Crystalline Solids**:
- Polar crystalline solids are composed of molecules that have a permanent dipole moment due to the unequal distribution of electron density. This results in one end of the molecule being slightly positive (δ+) and the other end being slightly negative (δ-).

2. **Identifying Intermolecular Forces**:
- In polar crystalline solids, the molecules are held together by intermolecular forces. The primary type of interaction that occurs between these polar molecules is known as dipole-dipole interactions.

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