Question

Which element is not considered as chalcogen?
A) Selenium
B) Oxygen
C) Sulphur
D) Polonium

Answer 1

We all know that chalcogens are the group $16$ elements present in the periodic table and they are so called because they have capability to form ores such as oxides and sulphides. We also know that the last element of the group is less reactive and thus unable to form much oxides and sulphides.

Complete solution:
As we know that the group $16$ elements are called oxygen family because oxygen is the first member of this group and the group $16$ elements are known as chalcogens meaning ore forming elements such as oxides and sulphides.
Among these elements oxygen is the most abundant followed by sulphur and the selenium and tellurium are found as metal selenides and tellurides in sulphide ores. And the last member Polonium occurs as a decay product of thorium and uranium minerals.
But polonium is a radioactive element and it is one of the rarest elements in the group. It is also harmful due to its radioactivity. So, except polonium, all other members of the group are chemically similar and form ions with $- 2$ oxidation state when they react with electropositive metals. Thus we can say that polonium is not considered as a chalcogen.

So, clearly we can conclude that the correct answer is Option D.

Note: Remember that chalcogen are present in the same group therefore possess similar electronic configuration and the solid and stable chalcogens so formed are soft in nature and do not have the ability to conduct heat very well. Chalcogens with higher atomic number possess a decreased electronegativity but their density, atomic radius, boiling point and melting points tend to increase.