A federal disclosure requirement for residential properties built prior to 1978 is:

The correct answer is the requirement for a lead-based paint disclosure. This requirement stems from the federal Lead-Based Paint Hazard Reduction Act, which mandates that sellers and landlords disclose information about lead-based paint and lead-based paint hazards in properties built before 1978. This law is crucial because lead exposure can have significant health impacts, particularly on young children and pregnant women. Therefore, it is vital for prospective buyers and renters to be informed about any potential lead hazards in a home.

The other options do not pertain to federal requirements specifically designed for properties built before 1978. For instance, while an energy efficiency audit relates to the performance of the property, it is not a mandatory disclosure under federal law. Similarly, a seller's disclosure of property condition is a general best practice in real estate transactions but is governed at the state level rather than federal law. Lastly, a water district notice is relevant in specific contexts, particularly regarding water rights or district regulations, but it does not relate to lead hazards or properties constructed before 1978.