The boiling point of water ____.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → depends on atmospheric pressure
A liquid boils when its vapour pressure becomes equal to the pressure above it. So the boiling point rises when the pressure on the water rises, and falls when it falls. Water boils at 100°C only at the normal atmospheric pressure of sea level.
On a high mountain the air pressure is lower, so water boils below 100°C and food takes longer to cook.
In a pressure cooker the pressure is higher, so water boils at about 120°C and food cooks faster.
Why the other options are incorrect
Option (1) is always 100°C — Incorrect. 100°C holds only at standard sea-level pressure; the boiling point changes with the pressure.
Option (3) depends on the material of the container — Incorrect. The container changes only how fast the water heats up, not the temperature at which it boils.
Option (4) depends on relative humidity — Incorrect. Humidity affects how fast water evaporates from its surface, not its boiling point.