ANS:A - boiling point (at the same pressure)

"Boiling point (at the same pressure)" refers to the temperature at which a liquid boils under specific atmospheric pressure conditions. In the context of Duhring's rule, it means the boiling point of the pure solvent (such as water) when the pressure remains constant. Here's a breakdown:

1. Boiling Point:
   • The boiling point of a substance is the temperature at which its vapor pressure equals the atmospheric pressure. At this temperature, bubbles of vapor form within the liquid and rise to the surface, causing the liquid to boil.
   • For example, the boiling point of pure water at standard atmospheric pressure (1 atmosphere) is 100°C (212°F).
2. At the Same Pressure:
   • When discussing the boiling point of a solution according to Duhring's rule, it's essential to keep the pressure constant. This means comparing the boiling points of the pure solvent and the solution under the same external pressure conditions.
   • Pressure affects the boiling point of a liquid: higher pressure increases the boiling point, while lower pressure decreases it. Therefore, to compare the boiling points of different substances accurately, the pressure must be held constant.
3. Duhring's Rule:
   • Duhring's rule states that the boiling point of a solution is a linear function of the boiling point of the pure solvent at the same pressure.
   • In other words, if you dissolve a solute in a solvent to create a solution, the boiling point of that solution will be higher than the boiling point of the pure solvent. The extent of the increase in boiling point depends on factors such as the concentration of the solute and its interaction with the solvent.
   • This rule is useful for predicting the boiling points of solutions based on the properties of the pure solvent.

Overall, "boiling point (at the same pressure)" emphasizes the importance of maintaining constant pressure conditions when comparing the boiling points of different substances, especially when applying Duhring's rule to predict the boiling points of solutions.