When a mass on a spring undergoes simple harmonic motion (SHM), its velocity is maximum as it passes through the equilibrium position.
This is because the restoring force is zero at the equilibrium position, and the maximum displacement occurs at this point. As the mass moves through the equilibrium position, the restoring force accelerates it, reaching its maximum speed at the equilibrium position. Therefore, the correct option is "is maximum."
In SHM, the restoring force acting on the object is directly proportional to its displacement from the equilibrium position and acts in the opposite direction. This type of motion is common in systems like springs.