Question 8: What happens to the frequency of a simple pendulum as the oscillation die down from large amplitude to a small one?
The amplitude of oscillation gradually decreases in the case of a damped oscillation. So the situation in question is of damped oscillation.
Now damping is caused by the resistance of the air (or any other medium) to the motion of the oscillator. The oscillator does work against this resistance force and gradually its energy is decreased. The resistive force not only decreases the amplitude of vibration but it also increases the time period of oscillation. Since frequency and time period are inversely proportional, the increased time period will decrease the frequency of oscillation.