Which FAR would list requirements for certification procedures for products, articles, and parts?

The correct choice is based on the fact that Part 21 of the Federal Aviation Regulations (FAR) specifically addresses the certification procedures for products, articles, and parts. This section outlines the requirements for obtaining type certificates, production certificates, and other approvals related to aviation products and components. It encompasses the essential criteria that manufacturers must meet to ensure their products are deemed safe and compliant with aviation standards.

Part 21 is fundamental because it establishes the framework under which the FAA grants these certifications, ensuring that all aviation products meet safety requirements before being approved for use. This is crucial for maintaining safety in the aviation industry and ensuring that all components meet the prescribed regulations.

On the other hand, Parts 43, 25, and 39 focus on different aspects of aviation regulation, such as maintenance practices, airworthiness standards for transport category airplanes, and airworthiness directives, respectively, but do not specifically deal with the certification requirements for products and parts in the same manner as Part 21 does.