Assertion : The use of hot air balloons in sports and for meteorological observations is an application of Charle's law
Reason : Hot air is less and hence gases expand on heating

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Answer

To solve the question, we need to analyze both the assertion and the reason provided, and determine their validity based on Charles's Law.

### Step 1: Understand Charles's Law
Charles's Law states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature (in Kelvin). This means that if the temperature of a gas increases, its volume will also increase, provided the pressure remains constant.

**Hint:** Remember that Charles's Law is about the relationship between temperature and volume at constant pressure.

### Step 2: Analyze the Assertion
The assertion states that the use of hot air balloons in sports and for meteorological observations is an application of Charles's Law. This is true because hot air balloons operate on the principle that when air inside the balloon is heated, it expands, becoming less dense than the cooler air outside. This difference in density allows the balloon to rise.

**Hint:** Think about how heating air affects its density and buoyancy in the context of hot air balloons.

### Step 3: Analyze the Reason
The reason provided states that "hot air is less dense and hence gases expand on heating." This statement is partially correct. Hot air is indeed less dense than cooler air, which is why it rises. However, the reason does not directly explain why gases expand on heating; rather, it describes the consequence of heating. The expansion of gases upon heating is a direct result of increased kinetic energy of the gas molecules, which is what Charles's Law describes.

**Hint:** Consider how the kinetic energy of gas molecules relates to temperature and volume.

### Step 4: Conclusion
Both the assertion and the reason are true. The assertion is correct because hot air balloons do utilize Charles's Law. The reason is also true, but it does not fully explain the assertion; it describes a related phenomenon. Therefore, while both statements are true, the reason is not a complete explanation of the assertion.

**Final Answer:** Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.