History of discovery: who first reported the experimental observation of nuclear fission in 1938, opening the path to chain-reaction physics?

Introduction / Context:
Nuclear fission’s experimental discovery transformed physics and engineering, enabling both civilian nuclear power and nuclear weapons. Knowing the key contributors and timeline is common in GK and engineering entrance exams.

Given Data / Assumptions:

• Year of discovery: 1938.
• Need the experimental observers who identified fission products.
• Other scientists listed contributed to related fields or theoretical insights.

Concept / Approach:
Otto Hahn and Fritz Strassmann bombarded uranium with neutrons and chemically identified barium among the products, implying the uranium nucleus had split. Lise Meitner and Otto Frisch provided the correct physical interpretation and coined “fission,” while Niels Bohr and John Wheeler developed theoretical frameworks. Rutherford pioneered nuclear physics earlier; Fermi led neutron physics and chain-reaction experiments subsequently. The first experimental observation belongs to Hahn and Strassmann.

Step-by-Step Solution:
Recall timeline: late 1938 chemical identification of barium from irradiated uranium.Associate the lab work with Hahn and Strassmann.Recognize interpretive contributions by Meitner and Frisch soon after.Select “Hahn and Strassmann.”

Verification / Alternative check:
Historical accounts consistently credit Hahn–Strassmann with the experimental proof; Meitner–Frisch gave the theoretical explanation and name; Fermi later achieved sustained chain reaction (1942).

Why Other Options Are Wrong:
Planck: Quantum theory pioneer, not fission discoverer.Rutherford: Earlier nuclear scattering & nucleus discovery, not fission observation.Fermi: Chain reaction and neutron physics, not the first fission observation.Bohr and Wheeler: Theoretical analysis, not the 1938 experiment.

Common Pitfalls:
Conflating first observation with later theoretical explanations or with the first controlled chain reaction (Chicago Pile-1, 1942).

Final Answer:
Hahn and Strassmann