Iron has several isotopes, which are variants of the element that have the same number of protons but different numbers of neutrons. The most stable and commonly occurring isotopes of iron are: 1. **Iron-54 (\(^{54}Fe\))**: This is the most abundant stable isotope, making up about 5.8% of natural iron.

Iridium has several isotopes, with the two most stable and naturally occurring ones being: 1. **Iridium-191 (Ir-191)**: This isotope has a half-life of about 19.17 hours and decays to stable osmium-191. It is a product of the decay of heavier elements and is not found in significant amounts in nature.

Iodine has several isotopes, the most notable of which are iodine-127, iodine-129, and iodine-131. 1. **Iodine-127 (¹²⁷I)**: This is the most stable and abundant isotope of iodine, making up about 100% of naturally occurring iodine. It has a half-life that is effectively infinite for practical purposes and is non-radioactive.

Indium has two stable isotopes: \(^{113}\text{In}\) and \(^{115}\text{In}\). 1. **\(^{113}\text{In}\)** - This isotope has a natural abundance of about 4.3%. It is a stable isotope, meaning it does not undergo radioactive decay. 2. **\(^{115}\text{In}\)** - This isotope is the most abundant, accounting for about 95.

Hydrogen has three main isotopes, which vary based on the number of neutrons present in the nucleus: 1. **Protium (^1H)**: This is the most abundant isotope of hydrogen, consisting of one proton and no neutrons. It is represented as \(^1H\) or simply H. 2. **Deuterium (^2H or D)**: This isotope contains one proton and one neutron, giving it a mass number of two.

Holmium (Ho) has one stable isotope, holmium-165 (Ho-165), which makes up nearly all naturally occurring holmium. In addition to this stable isotope, holmium has several radioactive isotopes, with varying half-lives. The most notable radioactive isotopes of holmium include: 1. **Holmium-163 (Ho-163)** - This isotope is used in various applications, including neutron capture therapy and as a source of gamma radiation.

Hassium (Hs) is a synthetic element with the atomic number 108. It is a member of the transactinide series of elements and is classified in Group 8 of the periodic table. As of my last knowledge update in October 2023, hassium has a few known isotopes, with all of them being radioactive.

Hafnium (Hf) is a chemical element with the atomic number 72 and has several isotopes. The isotopes of hafnium are distinguished by the number of neutrons in their nuclei, and they can be either stable or radioactive. Here are the key isotopes of hafnium: ### Stable Isotopes: 1. **Hafnium-174 (Hf-174)**: The most abundant stable isotope, making up about 32.5% of natural hafnium.

Gold (Au) has a few naturally occurring isotopes, the most common of which is gold-197 (^197Au). This isotope is stable and makes up nearly all naturally occurring gold. Gold-197 has an atomic mass of approximately 196.96657 u. In addition to ^197Au, there are several radioactive isotopes of gold, though they are not found in nature and are typically produced in laboratories or through nuclear reactions.

Germanium (Ge) has several isotopes, with the most stable and common ones being: 1. **Germanium-70 (¹⁷⁰Ge)**: This isotope has 32 neutrons and is stable. 2. **Germanium-72 (¹⁷²Ge)**: Also stable, this isotope has 34 neutrons. 3. **Germanium-73 (¹⁷³Ge)**: Another stable isotope with 35 neutrons.

Gallium has two stable isotopes, which are: 1. **Gallium-69 (¹⁶⁹Ga)**: This isotope has 39 neutrons and is the more abundant of the two stable isotopes, comprising about 60.11% of natural gallium. 2. **Gallium-71 (¹⁷¹Ga)**: This isotope has 41 neutrons and makes up about 39.89% of naturally occurring gallium.

Gadolinium (Gd) is a lanthanide element with atomic number 64 and has several isotopes. The most common isotopes of gadolinium include: 1. **Gadolinium-152 (Gd-152)**: This isotope has a natural abundance of about 0.14% and is stable. 2. **Gadolinium-154 (Gd-154)**: A stable isotope with a natural abundance of approximately 2.17%.

Francium is a highly radioactive alkali metal with the symbol Fr and atomic number 87. It is one of the least stable elements on the periodic table, and it has no stable isotopes. The isotopes of francium are all radioactive, and the most commonly discussed isotopes are: 1. **Francium-223 (Fr-223)**: This is the most stable and the most naturally occurring isotope of francium, with a half-life of about 22 minutes.

Fluorine has one stable isotope, which is fluorine-19 (¹⁹F). This isotope accounts for nearly all naturally occurring fluorine. Fluorine-19 has 9 protons and 10 neutrons in its nucleus. In addition to the stable isotope, fluorine has several radioactive isotopes, though they are not found in significant amounts in nature.

Flerovium (Fl) is a synthetic element with atomic number 114, and it is part of the superheavy elements in the periodic table. As of my last knowledge update in October 2023, there are very few known isotopes of flerovium, primarily because it is extremely unstable and has a short half-life.

Fermium (Fm) is a synthetic element with the atomic number 100. It is part of the actinide series in the periodic table. Isotopes of fermium are all radioactive, as fermium has no stable isotopes. The most notable isotopes of fermium include: 1. **Fermium-257 (Fm-257)**: This is the most stable isotope of fermium, with a half-life of about 100.5 days.

Europium (Eu) has a number of isotopes, but the most significant ones are Europium-151 and Europium-153, which are the only naturally occurring isotopes. 1. **Europium-151 (Eu-151)**: This isotope has an atomic mass of approximately 150.9198 u and has a natural abundance of about 47.8%. It is stable and does not undergo radioactive decay.

Erbium (Er) has several isotopes, with the most stable and common isotopes being: 1. **Erbium-162 (Er-162)**: This is the most abundant stable isotope, comprising about 33.5% of natural erbium. 2. **Erbium-164 (Er-164)**: This is another stable isotope, making up about 1.6% of natural erbium.

Einsteinium (Es) is a synthetic element with the atomic number 99. It has several isotopes, the most notable of which are: 1. **Einsteinium-253 (Es-253)**: This is the most stable isotope of einsteinium, with a half-life of about 20.5 days. It is produced in nuclear reactors and is used in research.

Dysprosium has several isotopes, but the most notable ones are: 1. **Dysprosium-156 (Dy-156)**: This is the most abundant stable isotope of dysprosium, making up about 5.3% of natural dysprosium. 2. **Dysprosium-158 (Dy-158)**: Another stable isotope, it accounts for approximately 0.1% of natural dysprosium.