Final answer:
The Federal Trade Commission (FTC) enforces provisions of the FD&C Act prohibiting the sale of products with false advertising, ensuring that advertisements do not contain untrue factual claims about a product's performance.
Step-by-step explanation:
The agency responsible for enforcing provisions of the FD&C Act that prohibit the sale of products with false advertising is the Federal Trade Commission (FTC). The FTC plays a crucial role in monitoring advertising practices to ensure that factual claims about a product's performance are accurate. While some exaggeration and ambiguity are permissible, outright falsehoods are not allowed. The FDA, which is often mentioned in the context of the FD&C Act, has a broader focus on the regulation of food, drugs, cosmetics, and associated products, rather than advertising practices. However, in cases of false or misleading statements that pertain to food or health benefits, the FDA would be involved in the enforcement action.