I. A liquid boils when its saturated vapour pressure is equal to the external pressure II. Dissolved substances in pure water lead to increase in the boilin...

The boiling point of a liquid is a physical property that describes the temperature at which a liquid changes to its vapor state. The peculiarities of boiling point of a liquid can be determined by considering the conditions that affect the boiling process. Statement I says that a liquid boils when its saturated vapor pressure is equal to the external pressure. This is a correct statement as it implies that a liquid will boil when the vapor pressure above the liquid becomes equal to the pressure surrounding the liquid. Statement II states that dissolved substances in pure water lead to an increase in the boiling point. This is also a correct statement. When a substance is dissolved in a liquid, it causes the boiling point of the liquid to increase. Statement III states that when the external pressure is increased, the boiling point increases. This is a correct statement as well. When external pressure is increased, the boiling point of a liquid also increases. Statement IV states that dissolved substances in pure water decrease the boiling point. This statement is incorrect as dissolved substances in pure water increase the boiling point of water. Therefore, the combination of statements that are peculiarities of the boiling point of a liquid are I, II, and III.