What is the typical response in a professional letter for indicating formal acknowledgement of request?

The appropriate choice for formally acknowledging a request in a professional letter is indeed to express gratitude for their inquiry. This response serves to confirm receipt of the request and shows appreciation for the communication. It establishes a professional tone and conveys that the sender values the correspondence, maintaining an open line of communication.

Utilizing this phrase not only acknowledges the request but also sets the stage for further information or action to follow, reinforcing a positive and respectful relationship between the parties involved.