Which is the longest and strongest bone in the human body?

The human skeleton consists of 206 bones of widely varying size and function. A bone's length is simply its measured span from one end to the other, while its strength is chiefly determined by how much compressive and tensile load it can bear without fracturing — a property driven by the bone's thickness, density, and how much of the body's weight it routinely carries.

The femur (thigh bone) runs from the hip joint to the knee joint. In an average adult it measures close to 45–50 cm, making it the single longest bone in the entire skeleton. It is also the principal weight-bearing bone of the lower limb — it transmits most of the body's weight down to the knee with every stride, briefly bearing close to the full body weight during the single-leg support phase of walking and running. This repeated high load has shaped it into a thick, dense, cylindrical bone capable of withstanding very high compressive forces, which is why it is also recognised as the strongest bone in the human body.

Checking this against the other leg and arm bones confirms the choice:

• Tibia (shin bone) — bears significant body weight in the lower leg but measures only around 36–40 cm, well short of the femur's length.

• Fibula — a thin, splint-like lower-leg bone that carries almost no body weight; its main role is muscle attachment and ankle stability, so it is neither long nor load-bearing.

• Humerus — the longest bone of the upper arm, but arm bones are shorter than the femur, so it does not hold the body-wide record.

Since the femur is the body's longest bone and its structure is built to withstand the greatest compressive forces of any bone during standing, walking, running, and jumping, it is recognised as both the longest and the strongest bone in the human body — making it the correct answer.