What is the function of the rear sight on a firearm?

The rear sight on a firearm serves a critical role in aiding the shooter to aim accurately. It achieves this function by providing a reference point for alignment with the front sight. When a shooter looks down the sights, the rear sight creates a notch or aperture through which the shooter can align the front sight and the target. This alignment is essential for improving accuracy, as it helps the shooter to center the target within their line of sight, making adjustments for elevation and windage as necessary.

The other functions mentioned in the choices are unrelated to the purpose of the rear sight. Stabilizing supports are part of the firearm's structure, while the housing of the firing mechanism and magazine retention are entirely different components that do not aid in aiming or sighting the firearm at a target.