Final answer:
The National Association of Realtors (NAR) is responsible for developing a Code of Ethics for its members, setting standards for professionalism and ethical conduct.
Step-by-step explanation:
The real estate trade organization known for developing a Code of Ethics for its members is the National Association of Realtors (NAR). This organization strongly upholds ethical practices within the real estate industry and ensures that its members adhere to the established standards of professionalism and ethical conduct. The other options provided, such as NAHB, CRE, and MLS do not match the abbreviation for this specific organization and its associated Code of Ethics.