Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: The first law of thermodynamics is based on law of conservation of mass. Reason R: Second law of thermodynamics states that heat flows from a higher temperature to lower temperature. In the light of the above statements, choose the most appropriate answer from the options given below
• Both A and R are correct and R is the correct explanation of A
• Both A and R are correct but R is NOT the correct explanation of A
• A is correct but R is not correct
• A is not correct but R is correct

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Important thermodynamics laws: First law: \[ \boxed{ \text{Conservation of energy} } \] Second law: \[ \boxed{ \text{Heat flows naturally from hot to cold} } \] Remember: \[ \boxed{ \text{First law tells “how much”, second law tells “which direction”} } \]

Answer 1

The Correct Option is D

Concept: Thermodynamics is governed mainly by:
• First law of thermodynamics
• Second law of thermodynamics The first law is associated with: \[ \boxed{ \text{Conservation of energy} } \] while the second law explains: \[ \boxed{ \text{Direction of heat transfer} } \] The question tests conceptual understanding of these laws.

Step 1: Analyzing Assertion A. Assertion A says: \[ \text{“The first law of thermodynamics is based on law of conservation of mass.”} \] This statement is incorrect. The first law of thermodynamics states: \[ \boxed{ \text{Energy can neither be created nor destroyed} } \] Mathematically: \[ \delta Q = dU + \delta W \] where:
• \(\delta Q\) = heat supplied
• \(dU\) = change in internal energy
• \(\delta W\) = work done Thus the first law is based on: \[ \boxed{ \text{Conservation of energy} } \] not conservation of mass. Hence: \[ \boxed{\text{Assertion A is incorrect}} \]

Step 2: Analyzing Reason R. Reason R states: \[ \text{“Second law of thermodynamics states that heat flows from higher temperature to lower temperature.”} \] This statement is correct. The Clausius statement of second law says: \[ \boxed{ \text{Heat naturally flows from hot body to cold body} } \] unless external work is supplied. Therefore: \[ \boxed{\text{Reason R is correct}} \]

Step 3: Selecting the appropriate option. We observe:
• Assertion A is incorrect
• Reason R is correct Thus: \[ \boxed{ (D)\ \text{A is not correct but R is correct} } \] Final Conclusion: The first law is based on conservation of energy, not conservation of mass, while the reason correctly states the natural direction of heat flow. Hence the correct answer is: \[ \boxed{ (D) } \]