The longest single bone in human is the

The femur (thigh bone) is the longest and strongest single bone in the human body. It extends from the hip joint to the knee joint and typically measures about one quarter of a person's total height.

The femur supports the weight of the body during standing, walking, and running, which is why it is both long and robust. Its length reflects the need for a large stride length in bipedal locomotion.

The other options are shorter bones with different functions:

• The humerus is the bone of the upper arm, extending from the shoulder to the elbow. It is the longest bone in the upper limb but is shorter than the femur.
• The scapula (shoulder blade) is a flat, triangular bone at the back of the shoulder. It is not a long bone at all.
• The sternum (breastbone) is a flat bone in the centre of the chest that connects to the ribs. It is relatively short compared to the femur.

For examination purposes, remember: femur = longest bone, and it is located in the thigh.