The smallest bone in the human body is called the Stapes. It is found in the middle ear and is one of the three tiny bones known as the ossicles. The Stapes is also called the "stirrup bone" because of its shape.

Here is a simple explanation:
- The Stapes is the tiniest bone, about 3 mm long.
- It helps in hearing by transmitting sound vibrations from the middle ear to the inner ear.
- Despite being small, it plays an important role in hearing.

Let’s understand the other bones:
- Tibia: This is a large bone in the lower leg.
- Femur: The longest and strongest bone in the thigh.
- Humerus: The bone of the upper arm.

So, the correct answer is the Stapes.

✅ Final Answer: Stapes.