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How many naturally occurring isotopes of Hydrogen are there?

This question was previously asked in
SSC Stenographer 2017 Previous Year Paper (14-Sep-2017) (Shift 1)
The correct answer is

3

Understanding Hydrogen Isotopes

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This difference in the number of neutrons means they have different mass numbers. The chemical properties of isotopes are generally very similar because they depend primarily on the number of electrons (which equals the number of protons in a neutral atom), but physical properties like mass, density, and diffusion rates can differ.

Naturally Occurring Hydrogen Isotopes

Hydrogen (\(\text{H}\)) is the simplest element, with just one proton. However, it has different naturally occurring isotopes based on the number of neutrons in its nucleus. There are three main naturally occurring isotopes of Hydrogen:

  1. Protium (\(^1\text{H}\)): This is the most common isotope of Hydrogen. Its nucleus contains just one proton and no neutrons. It has a mass number of 1. About 99.98% of naturally occurring Hydrogen is Protium.
  2. Deuterium (\(^2\text{H}\) or \(\text{D}\)): This isotope contains one proton and one neutron in its nucleus. It has a mass number of 2. Deuterium is often referred to as "heavy hydrogen". It makes up a small but significant fraction of natural hydrogen (around 0.015%).
  3. Tritium (\(^3\text{H}\) or \(\text{T}\)): This isotope contains one proton and two neutrons in its nucleus. It has a mass number of 3. Tritium is radioactive, undergoing beta decay with a half-life of about 12.32 years. While present naturally in trace amounts (formed by cosmic ray interaction with atmospheric gases), it is much rarer than Protium or Deuterium.

These three isotopes account for virtually all naturally occurring Hydrogen on Earth.

Summary of Hydrogen Isotopes

Isotope Name Symbol Number of Protons Number of Neutrons Mass Number Natural Abundance (Approx.) Stability
Protium \(^1\text{H}\) 1 0 1 99.98% Stable
Deuterium \(^2\text{H}\) or \(\text{D}\) 1 1 2 0.015% Stable
Tritium \(^3\text{H}\) or \(\text{T}\) 1 2 3 Trace amounts Radioactive

Based on the discussion, there are three naturally occurring isotopes of the element Hydrogen.

Revision Table: Hydrogen Isotopes Key Facts

Isotope Nucleon Composition Key Feature
Protium 1 Proton, 0 Neutrons Most abundant (>99.98%)
Deuterium 1 Proton, 1 Neutron Heavy hydrogen, stable
Tritium 1 Proton, 2 Neutrons Radioactive, trace amounts

Additional Information on Hydrogen Isotopes

Beyond the three naturally occurring isotopes, several other synthetic isotopes of Hydrogen have been produced in laboratories, such as Hydrogen-4, Hydrogen-5, Hydrogen-6, and Hydrogen-7. These are extremely unstable and decay very quickly.

Deuterium is used in various applications, including as a moderator in some nuclear reactors (in the form of heavy water, \(\text{D}_2\text{O}\)) and in nuclear fusion research. Tritium is used in self-luminous devices, as a radioactive tracer, and is also important in fusion research.

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