When it comes to the periodic table, elements are classified into various groups based on their chemical properties and atomic structures. Cerium, praesiodymium, and promethium belong to a particular group known as the rare earth elements.

The rare earth elements, also referred to as lanthanides, consist of 15 elements that span from atomic number 57 (lanthanum) to 71 (lutetium). These elements possess unique properties that make them valuable in various industries, including electronics, magnets, and catalysts.

Cerium, with the atomic number 58, is one of the most abundant rare earth elements. It is widely used in the production of catalytic converters for automobiles, as it can facilitate the conversion of harmful gases into less toxic substances. Additionally, cerium compounds are used in glass polishing, self-cleaning ovens, and as additives in fuel to improve combustion efficiency.

Praesiodymium, with the atomic number 59, is another member of the rare earth elements. It is primarily utilized in magnets, particularly in combination with neodymium to create powerful magnets used in electric motors and generators. These magnets are essential components in various applications, including wind turbines, hybrid vehicles, and computer hard drives.

Lastly, promethium, with the atomic number 61, is the rarest and least stable of the rare earth elements. It is radioactive and has no stable isotopes. Due to its radioactivity, promethium has limited practical uses and is mainly employed in research and medical applications, such as in the development of nuclear batteries and as a source of beta radiation for cancer treatment.

In conclusion, cerium, praesiodymium, and promethium belong to the group of rare earth elements or lanthanides. Each of these elements possesses distinct properties that make them valuable in various industries, contributing to advancements in technology and scientific research.

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