A liquid is heated up to a certain temperature. Which one of the following situation would correspond to the boiling of the liquid ?

Boiling is a phase transition where a liquid turns into vapor. This process occurs at a specific temperature known as the boiling point. Scientifically, a liquid begins to boil when its vapour pressure becomes equal to the external atmospheric pressure.

• Vapour Pressure: This is the pressure exerted by the gaseous molecules of a substance in equilibrium with its liquid phase. As the temperature of a liquid increases, its vapour pressure also increases.
• The Mechanism: When the vapour pressure reaches the level of the surrounding atmospheric pressure, bubbles of vapour can form within the bulk of the liquid and rise to the surface, rather than just evaporating from the surface.
• Altitude Effect: This relationship explains why water boils at lower temperatures at high altitudes; since atmospheric pressure is lower there, the vapour pressure required to match it is achieved at a lower temperature.

Thus, Option A accurately describes the physical condition necessary for boiling to occur.