In nuclear chemistry and physics, a hydrogen bomb (thermonuclear bomb) is based primarily on which fundamental principle?

Introduction / Context:
Nuclear weapons and energy involve two key processes: nuclear fission and nuclear fusion. Understanding the difference between them is a common requirement in general science and competitive exams. This question asks specifically about the hydrogen bomb, also known as a thermonuclear bomb, and which fundamental nuclear process it uses. Recognising that a hydrogen bomb is based on nuclear fusion of light nuclei, rather than on fission alone, is crucial.

Given Data / Assumptions:
- The device in question is a hydrogen bomb, also called a thermonuclear bomb. - Several nuclear processes are listed: nuclear fusion, nuclear fission, natural radioactivity, and artificial radioactivity. - We assume standard textbook definitions and descriptions of nuclear weapons. - The task is to identify the principle primarily responsible for the explosive energy of a hydrogen bomb.

Concept / Approach:
An atomic bomb based on uranium or plutonium uses nuclear fission, where heavy nuclei split into lighter fragments, releasing energy. A hydrogen bomb, in contrast, uses extremely high temperatures and pressures to fuse light nuclei such as isotopes of hydrogen (for example, deuterium and tritium) into heavier nuclei, releasing enormous energy. While a fission device is often used as a trigger to create the conditions for fusion, the defining principle of a hydrogen bomb is nuclear fusion. Therefore, the correct approach is to look for the option that mentions fusion of light nuclei.

Step-by-Step Solution:
Step 1: Recall that nuclear fusion is the process where two light atomic nuclei combine to form a heavier nucleus, with a loss of mass and a large release of energy. Step 2: Remember that in a hydrogen bomb, isotopes of hydrogen are fused under extreme conditions, which is why it is called a thermonuclear device. Step 3: Check option a, which states nuclear fusion of light nuclei into heavier nuclei. This matches the definition and the known working principle of a hydrogen bomb. Step 4: Option b, nuclear fission, correctly describes the principle of an atomic (fission) bomb, not a thermonuclear hydrogen bomb, so it is not the best answer here. Step 5: Options c and d refer to radioactivity in general, whether natural or artificially induced, which are related but not the defining process responsible for the hydrogen bomb's massive energy output. Step 6: Therefore, select option a as the correct answer.

Verification / Alternative check:
You can verify this by recalling that the Sun and other stars generate their energy mainly through nuclear fusion of hydrogen into helium. Hydrogen bombs attempt to mimic this stellar process on a very small and destructive scale, using a fission bomb as an initial trigger. Physics and chemistry textbooks consistently describe hydrogen bombs as thermonuclear fusion devices, not as pure fission or simple radioactive sources, confirming that nuclear fusion is the governing principle.

Why Other Options Are Wrong:
Option b, nuclear fission, is the correct principle behind atomic bombs such as those using uranium-235 or plutonium-239. Hydrogen bombs may use a fission stage to achieve the required conditions, but the main destructive energy comes from the subsequent fusion stage. Option c, natural radioactivity, refers to spontaneous decay of unstable nuclei and is not sufficient to explain the explosive yield of a hydrogen bomb. Option d, artificial radioactivity, involves creating radioactive isotopes through reactions, which is again not the central principle behind thermonuclear explosions. Thus, none of these options accurately captures the defining mechanism of a hydrogen bomb.

Common Pitfalls:
Students often confuse atomic bombs and hydrogen bombs and may pick nuclear fission out of habit. Another pitfall is to treat any nuclear process as equivalent and not distinguish between fission, fusion, and radioactivity. To avoid such mistakes, remember that atomic bombs are fission-based, while hydrogen bombs are fusion-based. The word hydrogen in the name should remind you that isotopes of hydrogen are being fused in the device.

Final Answer:
A hydrogen bomb is based on the principle of nuclear fusion of light nuclei into heavier nuclei.