The droplets of water observed around a bottle of milk taken out of the refrigerator is due to the fact that the?

Analysis

This question tests your understanding of phase changes and the kinetic theory of matter, specifically regarding how water vapour in the atmosphere interacts with cold surfaces.

Concept Explanation

The phenomenon described is condensation.

1. Water Vapour: The air around us contains invisible water vapour (gaseous water).
2. Kinetic Energy: Molecules in a gas possess kinetic energy, which keeps them in a gaseous state.
3. Heat Transfer: When this warm, moist air comes into contact with a cold surface (like a bottle of milk from the refrigerator), heat flows from the warmer air to the colder bottle.
4. Phase Change: As the water vapour molecules lose kinetic energy to the cold bottle, they slow down. When they lose enough energy, the intermolecular forces become strong enough to pull them together, turning the gas into liquid droplets on the surface of the bottle.

Step-by-Step Solution

• Step 1: Identify the state of the water. It starts as vapour (gas) in the air.
• Step 2: Identify the interaction. The cold bottle acts as a "heat sink," absorbing heat from the surrounding air.
• Step 3: Apply the principle of energy transfer. Since the bottle is cold, the water vapour molecules hitting the bottle lose energy to it.
• Step 4: Conclude the result. Losing energy causes the vapour to condense into liquid water droplets.

Looking at the options:

• A is incorrect because the vapour loses energy, it does not gain it.
• B describes the milk, but it does not explain why water forms on the outside of the bottle.
• C refers to boiling points, which is irrelevant here.
• D correctly identifies that the water vapour loses energy to the cold bottle, leading to condensation.

Conclusion

The correct answer is D.

Exam Tip

Whenever you see questions about "droplets" or "mist" forming on a cold surface, always look for the option that mentions loss of energy or cooling of the surrounding vapour. Remember: Condensation = Cooling = Loss of Energy.