Final answer:
The false statement is d. Focusing on GUI controls using the Tab key is controlled by the focus traversal policy, not by the order in which the controls were added. This policy can be customized by developers.
Step-by-step explanation:
The statement that is false among the provided options is: d. When you press the Tab key, the focus transfers from the current focusable control to the next one—this occurs in the order the controls were added to the GUI. This is incorrect because the focus traversal policy in most GUI frameworks, including JavaFX which utilizes GridPane's, is not necessarily based on the order in which controls are added. Instead, it is determined by the traversal policy, which can be overridden or configured by the developer.
Statement a. You can specify the default amount of space between a GridPane's columns and rows with its Hgap (horizontal gap) and Vgap (vertical gap) properties, respectively. is true. Developers can set the horizontal and vertical gaps to control the spacing between the elements within a GridPane.
Statement b. You can type in a TextField only if it's "in focus" is essentially correct, meaning that a TextField must be focused for user input to be entered into it.
Statement c. When you click an interactive control, it prompts for input is usually true as interactive controls, like buttons and text fields, are designed to accept user interaction, which includes prompting for input.