In basic atomic chemistry of hydrogen and its isotopes, which of the following statements is false?

Introduction / Context:
This question focuses on isotopes of hydrogen, which is one of the most fundamental topics in basic chemistry and nuclear science. Hydrogen has three main isotopes, namely protium, deuterium, and tritium, each with the same number of protons but different numbers of neutrons and therefore different masses. Competitive exams often test whether you remember the names, relative abundances, and simple properties of these isotopes. Here, you are asked to identify the one false statement among several correct statements about hydrogen isotopes. This requires accurate recall of which isotope is most abundant and what is meant by heavy hydrogen.

Given Data / Assumptions:
- The question presents four statements about hydrogen and its isotopes.
- You must decide which statement is factually incorrect according to standard chemistry knowledge.
- It is assumed that you know the basic composition and abundances of protium, deuterium, and tritium.
- Only one statement is false; the others are true and consistent with scientific data.

Concept / Approach:
The core concept involves isotopes, which are atoms of the same element with the same number of protons but different numbers of neutrons. Hydrogen has three commonly discussed isotopes. Protium, written as hydrogen 1, has one proton and no neutrons and is by far the most abundant isotope in nature. Deuterium, hydrogen 2, has one proton and one neutron and is known as heavy hydrogen because it has roughly double the mass of protium. Tritium, hydrogen 3, has one proton and two neutrons and is radioactive. The approach is to check each given statement against these facts to see which one contradicts well established information.

Step-by-Step Solution:
Step 1: Recall that protium has one proton and zero neutrons and makes up the vast majority of natural hydrogen, well over 99 percent. Step 2: Remember that deuterium has one proton and one neutron, doubling its mass relative to protium and earning the name heavy hydrogen. Step 3: Note that tritium has one proton and two neutrons, which means its mass is approximately three times that of protium. Step 4: Compare the statements. Saying that a normal hydrogen atom is roughly a third of the mass of tritium is reasonable because tritium has about triple the mass of protium. Step 5: Confirm that deuterium being called heavy hydrogen and having one neutron are both correct statements. Step 6: Evaluate the statement that protium is the rarest isotope. This is clearly false because protium is actually the most abundant isotope of hydrogen in the universe. Step 7: Therefore, identify the false statement as the one that claims protium is the rarest isotope of hydrogen.

Verification / Alternative check:
You can verify these facts by checking a standard chemistry textbook or periodic table reference. These sources will state that protium is the dominant form of hydrogen, deuterium is present in very small amounts, and tritium is extremely rare and radioactive. They will also mention that deuterium is known as heavy hydrogen and has one neutron. Simple mass comparisons also support the idea that protium has roughly one third the mass of tritium. Therefore, any claim that protium is the rarest isotope contradicts well established data and must be considered false.

Why Other Options Are Wrong:
The statement that hydrogen atom is roughly a third of the mass of tritium is essentially correct because tritium contains two additional neutrons compared to protium, making its mass about three times larger. Deuterium is indeed called heavy hydrogen because it weighs more than protium due to the presence of one neutron. The statement that deuterium atom has one neutron is also accurate. None of these statements conflict with standard isotope descriptions, so they are not false and therefore not the desired answer.

Common Pitfalls:
A common mistake is to mix up abundance with mass. Some students think that the heavier isotopes must be more important or more common, which can lead them to accept the idea that protium is rare. Others may vaguely remember that heavy hydrogen is unusual and mistakenly apply that label to the wrong isotope. Confusion between names and mass numbers is also frequent. To avoid such pitfalls, always link the names protium, deuterium, and tritium with their actual compositions and relative abundances. Remember clearly that protium dominates, deuterium is rare but stable, and tritium is very rare and radioactive.

Final Answer:
The false statement is that Protium is the rarest isotope of hydrogen.