When we allow a pendulum to swing, it comes to rest eventually. The reason behind this is

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It slows down because of the earth’s magnetic field

It slows down due to friction and air resistance

It does not obey the Law of conservation of energy

It gets heavier as it moves

answer is B.

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Detailed Solution

When we allow a pendulum to swing, it comes to rest eventually. The reason behind this is slowing down due to friction and air resistance
Let's use an example to better understand this: imagine a pendulum bob suspended from a string at point B at first, hanging motionlessly. The bob will gain potential energy due to an increase in height if we lift it to point A without letting the string slip. Once released, it will swing to point B, where its potential energy will start to decline, and it will gain kinetic energy from motion. It will once more begin to rise after point C, gaining potential energy and losing kinetic energy along the way.
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However, what's interesting to note is that point C's height is lower than point A's, and this trend will continue until point B, where the pendulum bob will once more come to rest.
The cause of this is that the air resists the bob while it swings, and the bob continuously loses some of its energy through collisions with dust particles, which are then dissipated into the surroundings. The bob loses height with each swing due to this energy loss, which eventually brings it to rest.
Since the energy lost by the bob is being transferred to its surroundings, the law of conservation of energy is not being violated, as can be seen.

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