Isotopes of hydrogen in nuclear science: Which one of the following is the radioactive isotope of hydrogen frequently used as a tracer in fusion and environmental studies?

Introduction / Context:
Hydrogen exists as several isotopes with different numbers of neutrons. Understanding which isotope is radioactive is essential for topics such as fusion reactions, radiolabeled tracers, and health physics. This question focuses on identifying the radioactive hydrogen isotope used widely in research and technology.

Given Data / Assumptions:

• Three common isotopic forms: protium (¹H), deuterium (²H or D), and tritium (³H or T).
• Ortho-hydrogen refers to a spin isomeric form of H2, not an isotope.
• We need the isotope that is radioactive.

Concept / Approach:
Isotopes share the same number of protons but differ in neutrons. Deuterium (one neutron) is stable and used in heavy water. Tritium (two neutrons) is unstable and radioactive, undergoing beta decay to helium-3. Ortho/para hydrogen describe nuclear spin configurations (parallel vs. antiparallel) in molecular hydrogen and are not isotopic distinctions.

Step-by-Step Solution:
Identify isotopes: D (stable), T (radioactive).Recognize that ortho-hydrogen is a spin isomer, not an isotope.Therefore, the radioactive isotope is tritium (³H).

Verification / Alternative check:
Nuclear data tables list tritium half-life ≈ 12.3 years with low-energy beta emission, confirming its radioactivity and utility as a tracer and in self-luminous devices.

Why Other Options Are Wrong:
Deuterium: stable; used in D2O and fusion targets but not radioactive. Ortho-hydrogen: not an isotope. “None of these” is incorrect because tritium is indeed radioactive.

Common Pitfalls:

• Confusing isotopes (D, T) with spin isomers (ortho/para).
• Assuming all heavy forms of hydrogen are radioactive; deuterium is stable.

Final Answer:
Tritium