Assertion : The Carnot cycle is useful in understanding the performance of heat engines. Reason : The Carnot cycle provides a way of determining the maximum possible efficiency achievable with reservoirs of given temperatures.

• Correct answer
  A

  If both assertion and reason are true and reason is the correct explanation of the assertion
• B

  If both assertion and reason are true but reason is not the correct explanation of the assertion
• C

  If assertion is true, but reason is false
• D

  Both assertion and reason are false statements.

Hence, the correct answer is option: 'A'.