Which law, enacted in 1950, categorized every South African into one of four racial groups?

The Population Registration Act, enacted in 1950, is the correct answer because it was a cornerstone of apartheid legislation that legally classified individuals into one of four racial categories: White, Black (African), Coloured, and Indian. This classification was crucial for enforcing the apartheid regime's policies, as it determined access to various rights, privileges, and services based on one's designated racial group. The act served as a foundational framework for further discriminatory laws and practices that aimed to segregate and control the movement and socioeconomic status of South African citizens based on race.

The other laws listed did not categorize individuals in the same way. The Bantu Education Act focused on controlling and limiting the education provided to Black South Africans, reinforcing educational segregation. The Morality Act aimed to regulate interpersonal relationships and marriages across racial lines but did not involve formal classification of individuals into racial groups. Influx Control laws were designed to control the movement of Black South Africans into urban areas but were not about categorizing individuals specifically by race. Thus, only the Population Registration Act is directly related to the legal classification of racial groups in South Africa.