Isotopic effects: hydrogen (protium) differs from deuterium primarily in which type of properties, while remaining largely similar in the others?

Introduction / Context:
Isotopes of an element have the same number of protons but different numbers of neutrons, leading to different masses. Mass differences produce noticeable physical property changes (density, diffusion rate, boiling point) while chemical properties remain broadly similar because electron structure is the same.

Given Data / Assumptions:

• Hydrogen (protium, ^1H) vs deuterium (^2H or D).
• We compare radioactive, physical, and chemical properties at ordinary conditions.
• Neither protium nor deuterium is radioactive; tritium (^3H) is the radioactive isotope of hydrogen.

Concept / Approach:
Isotopic substitution changes mass-related properties: heavier isotopes tend to have higher boiling/melting points and lower diffusion coefficients. Chemical reactivity patterns are mostly preserved but kinetic isotope effects can alter reaction rates. Since neither ^1H nor ^2H is radioactive, “radioactive properties” are not a distinguishing factor.

Step-by-Step Solution:

Verification / Alternative check:
Experimental data show D2O has higher boiling point and density than H2O. Reaction kinetics with C–H vs C–D bonds illustrate kinetic isotope effects without fundamentally changing qualitative chemistry.

Why Other Options Are Wrong:

• Radioactive properties: both are stable; tritium is the radioactive isotope.
• Chemical properties: broadly similar; differences are secondary (kinetic), not primary.
• All of the above: incorrect because (a) is false.
• Nuclear stability only: both are stable; not a differentiator.

Common Pitfalls:
Assuming isotopes always have notably different chemistry; conflating deuterium with tritium.

Final Answer:
Physical properties