Final answer:
The minimum thickness of a board to support a junction box is not explicitly given among the options; it is determined by local building codes and the NEC for compliance and safety.
Step-by-step explanation:
The minimum thickness of a board that may be used to support a junction box is none of the above. Junction box support requirements, including the thickness of the supporting material, are specified by local building codes and national electrical codes such as the National Electrical Code (NEC) in the United States. It's crucial for safety and compliance to refer to these codes when determining the necessary specifications for electrical installations.