Which of the following is a common issue if a furnace will not light due to a clogged pilot assembly orifice?

The situation described in the question indicates that the furnace is not lighting, and a clogged pilot assembly orifice is specifically mentioned. The rationale for identifying "clogged orifice" as the correct response lies in understanding the function of the pilot assembly and how it interacts with gas supply and ignition.

The pilot assembly orifice is the small opening through which gas flows to the pilot light. If this orifice becomes clogged with debris or soot, it restricts or completely blocks the gas flow, preventing the pilot light from igniting. This blockage directly affects the ability of the furnace to light since there would be insufficient gas supply to create the flame necessary for the pilot.

While inadequate gas supply, faulty ignition board, and insufficient venting are all important factors to consider when diagnosing furnace issues, they are not directly related to the specific problem stated in the question regarding the clogging of the pilot assembly orifice. The presence of a clogged orifice solely explains the failure to light, making it the most pertinent choice in this context.