Final answer:
The Marvelettes' most noteworthy song is "Please Mr. Postman". It became a number one hit on the Billboard Hot 100 chart and helped establish the Marvelettes as a significant Motown act.
Step-by-step explanation:
The Marvelettes were an American girl group in the 1960s, known for their contributions to the Motown sound. Their most noteworthy song is often considered to be "Please Mr. Postman". It was their debut single and became a number one hit on the Billboard Hot 100 chart, making them the first Motown act to achieve this feat. The song's catchy melody, harmonies, and relatable lyrics resonated with audiences and established the Marvelettes as significant players in the music industry.