Question

At Least how many known allotropes does selenium have?
a) $4$
b) $5$
c) $6$
d) $2$

Answer 1

Allotropes are the various structural forms of an element. As they differ in structure they have different physical and chemical properties. Allotropes are chemically and thermodynamically stable. The elements that have stable allotropes are that of carbon.

Complete step by step answer:
Allotropy is seen in various elements such as tin, carbon, sulphur, phosphorus,selenium and many more.
Examples of allotropes of carbon are diamond and graphite.
Selenium:
Selenium is a chemical element that is placed in the $16th$ group and $4th$ period.
It is denoted by the symbol $Se$ .
It is a non metal with the atomic number $34$ .
The properties of selenium are similar to the properties of sulphur, arsenic and tellurium.
In the periodic table it is placed below tellurium and to the left of selenium is arsenic.
Sometimes it shows properties of both metal and nonmetals, thus it is considered as metalloid.
It was discovered by Swedish chemist in the year $1817$ .
The allotropes of selenium are present in two forms.
Grey allotrope is one of the most stable allotrope of selenium.
It is also known as trigonal selenium.
The structure of grey allotrope is crystalline.
It is formed by the mild heating of other allotropes of selenium.
This form of allotrope of selenium is a semiconductor.
Red allotrope
Red allotrope is formed during the electrolytic refining process of copper.
It is amorphous powder.
When it is heated rapidly it changes its color from red to black.
So, the correct answer is option D) $2$

Note: For the commercial use, the selenium is produced as the byproduct of the refining of the sulphide ores. Allotropes are mostly found in between group $13$ to group $16$ . Sometimes the allotropes of an element are stable than the element itself.