Answer :

Final answer:

The widest rail in a panel door is the bottom rail, which provides structural stability and prevents warping.

Explanation:

The widest of all rails in a panel door is the bottom rail. Panel doors, also known as stile-and-rail doors, are made with a combination of vertical stiles and horizontal rails that form a framework to support the door's panels. The bottom rail is typically designed to be wider than the other rails to provide additional structural stability and resistance to the higher forces exerted near the lower end of the door. This design also helps to prevent the door from warping and provides a solid base for the panels.