Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion $$A$$: A pendulum clock when taken to Mount Everest becomes fast.
Reason $$R$$: The value of g (acceleration due to gravity) is less at Mount Everest than its value on the surface of earth.
In the light of the above statements, choose the most appropriate answer from the options given below

The assertion states that a pendulum clock when taken to Mount Everest becomes fast.

It is reasoned that the value of g (acceleration due to gravity) is less at Mount Everest than on the surface of the earth.

Upon analysis, at higher altitude such as Mount Everest the gravitational acceleration decreases, so $$g$$ is indeed less there. Therefore, the reason is correct.

Analyzing the assertion further, we recall that the time period of a simple pendulum is:

$$T = 2\pi\sqrt{\frac{L}{g}}$$

Since $$g$$ decreases at Mount Everest, the time period $$T$$ increases (the pendulum oscillates more slowly). A longer time period means each swing takes more time, so the clock runs slow rather than fast, making the assertion incorrect.

The assertion is incorrect but the reason is correct, so the correct answer is Option D.