Which of the following describes a field that can be checked or unchecked?

The Check Box Widget is specifically designed to allow users to select an option by checking or unchecking it. This widget provides a binary choice, where each checkbox can exist in either a checked (active) or unchecked (inactive) state. This characteristic makes it suitable for scenarios where multiple selections may be made independently.

In terms of the other options, the Container Widget is primarily used for layout purposes and does not inherently allow users to make selections. The If Widget is a conditional statement used in logic to dictate the flow of the application but does not interact with user selections. The Radio Button Widget, while it also allows users to indicate a preference, enforces a single selection among a group of options, meaning users cannot check and uncheck multiple options like in the case of checkboxes. This functionality distinguishes the Check Box Widget as the sole element that meets the criteria of being able to be individually checked or unchecked.