Isotopes of hydrogen check: tritium (H-3) and deuterium (H-2) share the same count of which subatomic particle?

Introduction / Context:
Isotopes of a chemical element are defined by the same atomic number (Z) but different mass numbers (A). For hydrogen, the three common isotopes are protium (H-1), deuterium (H-2), and tritium (H-3). Recognizing what is identical and what differs between isotopes is fundamental to chemistry, nuclear physics, and reactor science.

Given Data / Assumptions:

• Tritium: Z = 1, A = 3.
• Deuterium: Z = 1, A = 2.
• Neutral atoms have equal numbers of electrons and protons, but ions may not.

Concept / Approach:
The defining feature of an element is its proton number Z. All isotopes of hydrogen have exactly one proton in the nucleus. They differ in neutron count: deuterium has one neutron; tritium has two neutrons. The number of nucleons (protons + neutrons) therefore differs as well. While neutral atoms of both isotopes have one electron, the question typically concerns nuclear composition, and electrons can vary with ionization state.

Step-by-Step Solution:
1) Identify constant across isotopes: proton count (Z) remains the same.2) Identify differences: neutron count and total nucleons change (A differs).3) Conclude that “protons” is the quantity that is the same for tritium and deuterium.

Verification / Alternative check:
Periodic table groupings are by Z, confirming that isotopes share proton number and chemical identity while differing by neutron number and nuclear mass.

Why Other Options Are Wrong:
Neutrons: D has 1, T has 2 → not the same.Electrons: can depend on ionization; not an intrinsic nuclear property.Nucleons: totals differ (2 vs 3).

Common Pitfalls:
Confusing atomic number with mass number; assuming electrons are fixed irrespective of charge state; overlooking that “nucleons” sums protons and neutrons.

Final Answer:
Protons