Question

Elements $O,S,Se$ and $Te$ are commonly known as:
A. Halogens
B. Rare earth elements
C. Chalcogens
D. Pnictogens

Answer 1

Chalcogens show similar patterns in electron configuration, especially in the outermost shells, where they all have the same number of valence electrons, resulting in similar trends in chemical behavior. The group 16 elements are also known as the chalcogens and have six electrons in their outermost shell.

Complete step by step answer:
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen ($O$ ), sulfur ($S$ ), selenium ($Se$ ), tellurium ($Te$ ), and the radioactive element polonium (Po). The chemically uncharacterized synthetic element livermorium (Lv) is predicted to be a chalcogen as well. The word "chalcogen" is derived from a combination of the Greek word khalkόs principally meaning copper (the term was also used for bronze/brass, any metal in the poetic sense, ore or coin.
Halogens are elements that have seven electrons in their valence shell or the group 17 elements.
Rare earth elements are defined by the International Union of Pure and Applied Chemistry, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium.
Pnictogens are members of the nitrogen group of elements, Group 15 of the periodic table (formerly numbered as Group V or Group VA). This group consists of nitrogen, phosphorus, arsenic, antimony, bismuth, and ununpentium.

Thus, the correct option is C. Chalcogens.

Note:
Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium.