Which federal agency oversees the operation of the health insurance marketplace?

The correct answer is the Centers for Medicare and Medicaid Services (CMS), which is the federal agency responsible for overseeing the operation of the health insurance marketplace. CMS plays a pivotal role in administering the health insurance programs, including Medicare and Medicaid, and managing the federal health insurance exchanges, also known as the marketplaces. Through the Affordable Care Act (ACA), CMS ensures that the marketplace operates effectively, providing individuals and families with access to affordable health insurance options.

The other agencies listed do not have this specific responsibility. The Federal Insurance Corporation does not exist in this context and does not manage health insurance marketplaces. The National Health Service is a UK-based public health service, unrelated to U.S. health insurance structures. The Department of Health and Human Services does oversee many aspects of healthcare and public health, but it is CMS that directly manages the marketplaces, making CMS the most specific and accurate answer to the question.