Which bone is found in the forearm and corresponds with the thumb?

The radius is the correct choice because it is one of the two bones located in the forearm, the other being the ulna. The radius is positioned on the same side as the thumb when the palm is facing upwards, which makes it specifically associated with the thumb's functionality. This bone plays a crucial role in the movement of the wrist and the hand, especially in actions involving the thumb.

The humerus is located in the upper arm and does not correspond to the forearm. The scaphoid is one of the carpal bones in the wrist and not a bone of the forearm. The ulna, while also a bone of the forearm, is on the opposite side of the radius and corresponds with the little finger, rather than the thumb. Thus, the radius is uniquely positioned to align with thumb movements and functions in the forearm.