Which one of the following substances does not have a melting point ?

Options

A. Bromine
B. Sodium chloride
C. Mercury
D. Glass

Explanation

To determine which substance does not have a melting point, we first need to understand what a melting point is. The melting point is the temperature at which a solid turns into a liquid.

Now, let's analyze the given options:

1. **Bromine (Br)**: Bromine is a liquid at room temperature. Since it is already in the liquid state, it does not have a melting point (it has a boiling point instead).

2. **Sodium Chloride (NaCl)**: Sodium chloride is a solid at room temperature, and it has a definite melting point where it transitions from solid to liquid.

3. **Mercury (Hg)**: Mercury is also a liquid at room temperature. Similar to bromine, it does not have a melting point but has a boiling point.

4. **Glass**: Glass is an amorphous solid, and while it does soften upon heating, it does not have a sharp melting point like crystalline solids do. Instead, it transitions gradually from solid to liquid.

Based on this analysis, the substances that do not have a melting point are:

- **Bromine**
- **Mercury**

Both of these substances are liquids at room temperature and do not have a defined melting point.

### Final Answer:
The substances that do not have a melting point are **Bromine** and **Mercury**.