Final answer:
The Plessy v. Ferguson decision established the legal standard that segregation can occur with 'separate but equal' facilities. The correct answer is option 4.
Step-by-step explanation:
The legal standard established by the Plessy v. Ferguson decision was segregation can occur with 'separate but equal' facilities.
In this landmark case, the Supreme Court ruled that racial segregation was constitutional as long as the separate facilities for Black and White people were equal in quality. This decision reinforced the practice of racial segregation and gave states the authority to determine who was White and who was non-White and to enforce separation in public accommodations.
This ruling had significant implications and solidified the concept of 'separate but equal' as the legal standard for segregation for the next several decades, leading to unequal treatment and opportunities for African Americans.