Which one of the following is an example of the force of gravity of th

Which one of the following is an example of the force of gravity of the earth acting on a vibrating pendulum bob ?

Applied force
Frictional force
Restoring force
Virtual force
This question was previously asked in
UPSC NDA-1 – 2018
When a pendulum bob is displaced from its equilibrium position, the force of gravity acting vertically downwards, combined with the tension in the string, results in a net force that pulls the bob back towards the equilibrium position. This force, which is always directed towards the equilibrium position and proportional to the displacement (for small angles), is known as the restoring force.
In simple harmonic motion, the restoring force is crucial as it is responsible for bringing the oscillating system back to its equilibrium state. For a simple pendulum, the component of gravity tangential to the arc of motion provides this restoring force.
Applied force is a general term for any external force. Frictional force opposes motion. Virtual force (or fictitious force) appears in non-inertial reference frames. Gravity itself is the fundamental force involved, but its component acting along the path of motion towards equilibrium is the restoring force in the context of oscillation.