What indicates a successful lock of the slide to the rear during the function check?

A successful lock of the slide to the rear during the function check is indicated by the slide follower pushing up on the slide stop. When the magazine is inserted into the firearm and emptied during cycling, the follower of the magazine engages the slide stop, which is designed to hold the slide in a rearward position. This action signifies that the slide has completed its cycle and is properly locked back, allowing for inspection and ensuring the firearm is clear of ammunition. This is a critical aspect of the function check, as it confirms both the magazine and slide stop mechanisms are operating correctly.

The other choices do not provide direct evidence of a successful lock of the slide. For example, the magazine sliding out freely pertains to how the magazine is removed and does not indicate the status of the slide. The decocking lever clicking into place relates to the safety features of the firearm but does not affect the slide's locking mechanism. The hammer moving back slightly may occur for various reasons during cycling but is not a direct indicator of the slide being properly locked to the rear.