What happens to the boiling point when external pressure increases?

• A. The boiling point rises with higher external pressure.
• B. The boiling point falls with higher external pressure.
• C. The boiling point remains the same regardless of pressure.
• D. The liquid will not boil under any external pressure.

Answer: (C)

Boiling point depends on the surrounding pressure. Boiling happens when a liquid’s vapor pressure equals the ambient pressure. If you raise the external pressure, the liquid must reach a higher temperature for its vapor pressure to match that pressure, so the boiling point increases. For example, water boils at about 100°C at 1 atmosphere, but at greater pressures it boils at temperatures higher than 100°C. If pressure is lowered, the boiling point drops. So the idea that the boiling point stays the same regardless of pressure isn’t correct, and it’s also not true that a liquid won’t boil under any pressure. The key point is: increasing external pressure raises the temperature required to boil.