Equal quantities (50 ml) of the following four samples of water are placed in four beakers of 100 ml capacity. Their boiling points are determined accurately using the same thermometer. Which sample of water will have the lowermost boiling point as compared to other three samples?

The boiling point of a liquid is a colligative property, meaning it depends on the concentration of dissolved solute particles [t1][t7]. When a non-volatile solute is added to a solvent like water, the vapor pressure decreases, requiring a higher temperature to reach the boiling point; this phenomenon is known as boiling point elevation [t3][t4]. Distilled water is the purest form of water among the options, containing negligible dissolved minerals or salts. In contrast, bottled mineral water, well water, and sea water contain varying levels of total dissolved solids (TDS) [t6]. Sea water has the highest salinity and thus the highest boiling point [c1][c4]. Since boiling point elevation is directly proportional to solute concentration [t3][t8], the sample with the fewest impurities—distilled water—will have the lowest boiling point, closest to the standard 100C of pure water.

Sources

1. [1] https://en.wikipedia.org/wiki/Boiling-point_elevation
2. [2] https://des.sc.gov/sites/des/files/Library/CR-006453.pdf
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Factors Affecting Temperature Distribution of Oceans > p. 512
4. [4] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 12: Water (Oceans) > SALINITY OF OCEAN WATERS > p. 104