What action should you take if your No. 1 VOR receiver malfunctions while operating in controlled airspace under IFR?

If the No. 1 VOR receiver malfunctions while operating in controlled airspace under IFR, reporting the malfunction immediately to ATC is the correct action because it ensures that air traffic control is aware of the situation. This communication allows ATC to assess your aircraft's navigation capabilities and make any necessary adjustments to your flight plan or provide assistance in managing traffic around you.

Reporting the VOR malfunction is crucial for maintaining safety and situational awareness within controlled airspace. It allows other controllers and pilots to understand that your navigation information may be compromised, which could impact air traffic management decisions and your flying environment.

Maintaining open communication with ATC enhances overall safety during IFR flights, as it ensures that everyone is aware of any potential navigation issues that could affect the safe operation of the flight. The other options either neglect reporting the issue or suggest actions that could compromise safety or visibility for both the pilot and other airspace users.