The grandfather clock will now run slow (Option A).
<h3>What is Time Period of an oscillation?</h3>- The time period of an oscillation refers to the time taken by an object to complete one oscillation.
- It is the inverse of frequency of oscillation; denoted by "T".
Now,
, where L is the length and g is the gravitational constant, is the formula for a pendulum's period.
- The period will increase as one climbs a very tall mountain because g will slightly decrease.
- Due to this and the previous issue, the clock runs slowly and it seems that one second is longer than it actually is.
Hence, the grandfather clock will now run slow (Option A).
To learn more about the time period of an oscillation, refer to the link: brainly.com/question/26449711
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