Isotopes of hydrogen: How many isotopes of hydrogen are commonly recognized in nuclear science?

Introduction / Context:
Hydrogen is unique for having well-known isotopes with important roles in chemistry, nuclear energy, and astrophysics. Recognizing how many isotopes are commonly referenced is fundamental background knowledge for students of physical science.

Given Data / Assumptions:

• We refer to commonly recognized isotopes: protium, deuterium, tritium.
• Protium (¹H) is stable; deuterium (²H) is stable; tritium (³H) is radioactive.

Concept / Approach:
An isotope is defined by the same atomic number (Z = 1 for hydrogen) and different neutron numbers. Protium has zero neutrons, deuterium has one, and tritium has two. While additional exotic hydrogen isotopes can be created (e.g., ⁴H), they are extremely short-lived and not commonly counted in basic curricula. Therefore, the accepted number for general education is three.

Step-by-Step Solution:

Verification / Alternative check:
Standard chemistry and physics texts enumerate the three principal isotopes, with deuterium used in heavy water and tritium in fusion research.

Why Other Options Are Wrong:

• No/one/two: Understate the accepted set of isotopes used in science and technology.

Common Pitfalls:
Confusing “stable isotopes” (two) with “commonly recognized isotopes” (three). The question is not restricted to stability.

Final Answer:
Three