* Pure substances have a specific boiling point: This is true at a given pressure (usually standard atmospheric pressure). Each pure substance has a characteristic boiling point, meaning it will transition from liquid to gas at that particular temperature.

* Pressure affects boiling point: This is important! The boiling point of a substance is the temperature at which its vapor pressure equals the surrounding pressure. So, at higher pressures, the boiling point is also higher. This is why water boils at a lower temperature on a mountain top.

* Impurities can affect boiling point: While a pure substance has a defined boiling point, impurities can cause the boiling point to change slightly. This is because the presence of other substances can alter the intermolecular forces within the liquid, making it easier or harder for molecules to escape into the vapor phase.

In conclusion: A pure substance will have a specific boiling point at a given pressure. However, the boiling point can be influenced by pressure and the presence of impurities.