RESPA would apply to which of these?

RESPA, or the Real Estate Settlement Procedures Act, applies primarily to transactions involving federally related mortgage loans, which include most residential loans that are used to purchase homes. The correct answer corresponds with a second mortgage on a condominium because this type of financing typically involves the purchase of residential real estate, thus falling under RESPA regulations.

In contrast, a home equity line of credit is typically exempt from RESPA’s rules since it doesn't involve a purchase transaction. A conventional loan, while it does relate to residential financing, is not specifically the best example in the context of the question as it could refer to various types of loans, not all of which may be subject to RESPA. Lastly, commercial property finance is definitively outside the scope of RESPA, as the act is designed to protect consumers in residential mortgage transactions, not in commercial transactions. Hence, the second mortgage on a condominium aligns with the applicability of RESPA, making it the correct answer.