(1901-1954) was an Italian-American physicist who created the Chicago Pile-1, the world's first nuclear reactor.

• A. Enrico Fermi
• B. Albert Einstein
• C. Niels Bohr
• D. Ernest Rutherford

Answer: (A)

The main idea this question tests is knowing who achieved the first controlled, self-sustaining nuclear chain reaction and where it happened. Enrico Fermi, an Italian-American physicist, led the team that built Chicago Pile-1, the first nuclear reactor. In 1942, under his direction, CP-1 achieved the first sustained nuclear chain reaction, demonstrating that a controlled release of nuclear energy was possible. This milestone was pivotal for both science and the Manhattan Project.

Albert Einstein did influential theoretical work and his letter helped spur interest in atomic research, but he did not build the reactor. Niels Bohr contributed foundational ideas about atomic structure and quantum theory and advised on early nuclear discussions, but he did not construct CP-1. Ernest Rutherford discovered the nuclear nature of atoms, but again, he did not build the reactor.