What does the melting point of a pure substance signify?

The melting point of a pure substance is a characteristic physical property that is consistent under specific conditions, such as atmospheric pressure. It signifies the temperature at which the solid form of a substance transitions to its liquid form. This property is very useful for identification purposes because each pure substance has a specific melting point. When you measure the melting point of a sample and compare it to known values for pure substances, you can determine the identity of that substance.

In practice, pure substances will have a sharp and well-defined melting point, while mixtures or impure substances will typically exhibit a wider range of melting temperatures. Therefore, option B accurately reflects the significance of melting point as a definitive characteristic that can help reliably identify materials when conducted under controlled conditions.