Which of the following will increase the boiling point of water? I. Taking it to a high altitude II…

To solve this problem, we need to understand the factors that influence the boiling point of a liquid. Boiling occurs when the saturated vapour pressure of a liquid equals the external atmospheric pressure.

1. Analyze the options

• I. Taking it to a high altitude: At high altitudes, atmospheric pressure is lower. Since boiling point decreases as external pressure decreases, this will lower the boiling point.
• II. Dissolving a salt into it: Adding a solute (like salt) to a solvent (water) causes "boiling point elevation." The solute particles interfere with the escape of water molecules into the vapour phase, requiring more heat to reach the boiling point. This increases the boiling point.
• III. Heating it in a sealed flask: In a sealed flask, the vapour produced cannot escape. As the temperature rises, the pressure inside the flask increases above atmospheric pressure. Since boiling point increases with pressure, this increases the boiling point.
• IV. Increasing the rate of heat supply: Increasing the heat supply only makes the water boil faster (the rate of evaporation increases), but it does not change the temperature at which the water boils. The boiling point remains constant once reached.

2. Explain the concept

• Boiling Point Elevation: The presence of impurities or solutes increases the boiling point of a liquid.
• Pressure-Boiling Point Relationship: The boiling point of a liquid is directly proportional to the external pressure exerted on its surface. Increasing the pressure (as in a pressure cooker or a sealed container) increases the boiling point.

3. Show the solution

• Statement I is incorrect because lower pressure decreases the boiling point.
• Statement II is correct because solutes elevate the boiling point.
• Statement III is correct because a sealed container traps vapour, increasing the pressure and thus the boiling point.
• Statement IV is incorrect because the rate of heating does not change the boiling point temperature.

Therefore, only statements II and III will increase the boiling point of water.

4. Identify the answer

Comparing our findings with the provided options, the correct choice is C.

5. Exam Tip

Remember the "Pressure-Boiling" rule: If you want to cook food faster (like beans), you use a pressure cooker. The pressure cooker traps steam, increasing the pressure inside, which raises the boiling point of water above $100^\circ\text{C}$. Higher temperature means the food cooks faster!