Final answer:
The biceps brachii muscle is the prime mover for flexion of the arm.
Step-by-step explanation:
The biceps brachii muscle is the prime mover for flexion of the arm. It is located in the upper arm and crosses both the shoulder and elbow joints.
The biceps brachii is responsible for flexing the forearm and also helps in supinating the forearm at the radioulnar joints and flexing the arm at the shoulder joint.