When trying to turn a key into a lock, following is applied

Answer: Option D

Imagine you're trying to open a door with a key.
You're not just pushing or pulling straight (that would be a force).
Instead, you're twisting the key.
This twisting action is what we call a moment in engineering.
A moment is a turning effect caused by a force acting at a distance from a pivot point (in this case, the center of the lock).
It's like a force trying to rotate something.
So, the correct answer is a moment because it describes the turning action you apply to the key in the lock.
Coplanar forces act in the same plane, which isn't what happens when you turn a key.
Non-coplanar forces act in different planes, also not applicable here.
A couple is two equal and opposite parallel forces, which also doesn't represent the action of turning a key.