Question

Given below are two statements :
Statement (I) : The refrigerant is one whose boiling point at normal atmosphere pressure is lower than the temperature we wish to obtain.
Statement (II) : When the pressure on a liquid is decreased it will boil (burn into vapor) at a much lower temperature.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

This relationship between pressure and boiling point is why water boils at a lower temperature at high altitudes (lower atmospheric pressure) and takes longer to cook food unless using a pressure cooker.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Refrigeration relies on thermodynamics, where a fluid (refrigerant) constantly changes phases between liquid and gas to absorb and release heat.
This cycle is regulated by controlling the temperature and pressure of the system.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Statement (I): "The refrigerant is one whose boiling point at normal atmospheric pressure is lower than the temperature we wish to obtain."
For a refrigeration system to cool an area, the liquid refrigerant must evaporate (boil) inside the evaporator coils at a temperature below the target compartment temperature.
This temperature difference allows the refrigerant to absorb heat from the food or air inside the refrigerator.
Therefore, the refrigerant's boiling point at standard pressure must be lower than the target cooling temperature. (True)
- Statement (II): "When the pressure on a liquid is decreased it will boil at a much lower temperature."
In physics, the boiling point of a liquid is directly related to the surrounding pressure.
When pressure is reduced (such as in the expansion valve of a refrigerator), the molecules require less thermal energy to overcome atmospheric resistance and transition into a gas.
This allows the liquid to boil at a much lower temperature. (True)
Therefore, both Statement (I) and Statement (II) are true.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are true, corresponding to option (A).