Identify the intermolecular forces that must be overcome to cause the melting of the following solids. Also arrange the solids in increasing order of melting points.
(a) NaF (b) HF (c) HCl (d) `Cl_(2)`

Explanation

To solve the problem of identifying the intermolecular forces that must be overcome to cause the melting of the given solids and arranging them in increasing order of melting points, we will analyze each solid one by one.

### Step-by-Step Solution:

1. **Identify the nature of each solid:**
- (a) **NaF**: Sodium fluoride is an ionic compound. It consists of Na⁺ and F⁻ ions held together by strong ionic bonds.
- (b) **HF**: Hydrogen fluoride is a molecular solid that exhibits hydrogen bonding due to the presence of a hydrogen atom bonded to a highly electronegative atom (fluorine).
- (c) **HCl**: Hydrogen chloride is also a molecular solid, but it exhibits dipole-dipole interactions as it is a polar molecule, but does not have hydrogen bonding like HF.
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